JP5810994B2 - COMMUNICATION DEVICE AND COMMUNICATION DEVICE ADJUSTING METHOD - Google Patents

Description

  The present invention relates to a communication device and a method for adjusting an antenna provided in the communication device.

  In order to improve frequency utilization efficiency, a multiple input multiple output (MIMO) scheme may be used. A terminal that supports the MIMO scheme includes a plurality of antennas, and can perform communication using a plurality of channels simultaneously between the terminal and the base station. However, when the terminal includes a plurality of antennas, there is a problem that reception performance deteriorates due to coupling between the antennas. For example, in a terminal equipped with the antenna A and the antenna B, the signal transmitted from the antenna A may be absorbed by another antenna B, so that the reception performance may be deteriorated. Therefore, in order to reduce the amount of coupling between the plurality of antennas, the impedance of the coupling reduction circuit is adjusted.

  As a related technique, a method of adjusting the reactance value of the variable reactance element so that the objective function representing the power of the received signal is substantially maximized has been proposed. By adjusting the reactance value, the main beam of the array antenna is directed in the direction of the desired wave, and null is directed in the direction of the interference wave. There are also several proposals for a method of selecting an antenna beam. For example, a particular antenna beam combination is selected to maximize the average signal-to-interference plus noise ratio (SINR) of the RF signal received via the multi-radio signal propagation path Communication devices have been proposed. There has also been devised a communication device including an antenna beam selection control unit that controls antenna selection for signal transmission and / or reception based on channel evaluation acquired for each basic antenna beam radiation pattern.

JP 2003-304112 A JP 2007-300606 A JP 2008-61238 A

  Even if the amount of coupling between a plurality of antennas is controlled, if the impedance of each antenna is not adjusted to an appropriate value, there is a problem that reception performance cannot be improved. In recent years, since an antenna is often mounted inside a terminal, the impedance of the antenna tends to fluctuate depending on the usage status of the terminal. Since the throughput is good when the antenna performance is good, it is desirable to improve the antenna performance efficiently. In addition, in any of the methods described in the background art, it is impossible to specify which of the circuits that can be prepared to effectively improve the performance of the antenna, so that it is impossible to perform efficient control. There is. In the background art, the case of MIMO has been described. However, it is desirable to efficiently improve reception performance when a communication apparatus including a plurality of antennas is used, not limited to MIMO.

  An object of this invention is to provide the communication apparatus which can improve receiving performance efficiently.

  The communication apparatus according to the embodiment includes a first antenna, a second antenna, a first adjustment circuit, a second adjustment circuit, a first interference power calculation unit, a second interference power calculation unit, a correlation calculation unit, A selection unit and a circuit control unit are provided. The first adjustment circuit adjusts the gain of the first antenna. The second adjustment circuit adjusts the gain of the second antenna. The first interference power calculation unit calculates first interference power received from the first antenna. The second interference power calculation unit calculates second interference power received from the second antenna. The correlation calculation unit calculates a correlation value between the reception signal of the first antenna and the reception signal of the second antenna. The selection unit uses the evaluation value to select an adjustment circuit that has a greater influence on the reception performance. The evaluation value is calculated using the first interference power, the second interference power, and the correlation value. Also, the evaluation value is positive if the influence of the gain of the second antenna on the reception performance is larger than the influence of the gain of the first antenna on the reception performance via the first and second antennas. Takes the value of The circuit control unit preferentially adjusts the selected adjustment circuit so that the reception performance is improved.

  The reception performance of the communication device can be improved efficiently.

It is a figure explaining the example of the control performed with the communication apparatus which concerns on embodiment. It is a figure which shows the example of the communication apparatus which concerns on 1st Embodiment. It is a figure which shows the example of the hardware constitutions of the communication apparatus which concerns on 1st Embodiment. It is a figure which shows the example of the relationship between adjustment amount and the electric power of a signal. It is a flowchart explaining the example of the operation | movement performed in 1st Embodiment. It is a figure which shows the example of the communication apparatus which concerns on 2nd Embodiment. It is a figure which shows the example of the relationship between adjustment amount and a correlation value. It is a flowchart explaining the example of the operation | movement performed in 2nd Embodiment. It is a figure which shows the example of a structure of the communication apparatus which concerns on 3rd Embodiment. It is a flowchart explaining the example of the determination performed by the selection part. It is a flowchart explaining the example of operation | movement of the selection part in 4th Embodiment. It is a figure which shows the example of the eigenvalue and transmission characteristic of MIMO. It is a figure which shows the example of the relationship between the magnitude | size of a 1st eigenvalue, and the correlation value of the received signal between antennas. It is a figure which shows the example of the relationship between the magnitude | size of a 1st eigenvalue, and the gain difference between antennas. It is a figure which shows the example of the relationship between the channel capacity of MIMO and SINR. It is a flowchart explaining the example of operation | movement of the selection part in 5th Embodiment. It is a flowchart explaining the modification of operation | movement of a matching circuit control part.

FIG. 1 is a diagram illustrating an example of control performed by the communication apparatus according to the embodiment. FIG. 1 shows an example in which a communication apparatus receives a signal S from a communication destination base station. Communication device comprises an antenna A1 and A2, the gain of the antenna A1 is the gain of _{G 1,} the antenna A2 is assumed to be _{G 2.} Further, the propagation coefficient representing the status of the propagation path from the base station to the antenna A1 is H _1, the propagation coefficients that represent the status of the propagation path from the base station to the antenna A2 is assumed to be H _2. In addition to the signal S received from the base station, the communication device also receives noise. Noise received by the communication device is divided into two types, external noise (I) and internal noise (N). The internal noise N is noise generated by operations of a central processing unit (CPU) and a memory included in the communication device. The external noise is a signal other than the signal S that is to be received by the communication device among the signals received by the communication device. Therefore, the communication apparatus adjusts so that the ratio (SINR) of the signal S to the sum of the external noise power and the internal noise power is increased to improve the reception performance of the communication apparatus.

  The communication apparatus has a first function that is directly proportional to a value obtained by subtracting the SINR (SINR1) when the gain of the antenna A1 is k times from the SINR (SINR2) when the gain of the antenna A2 is k times. Store as evaluation function. k is set according to the implementation and can take any value greater than 1. Here, since the value of the first evaluation function is directly proportional to SINR2−SINR1, the value of the first evaluation function is positive. The fact that the gain of the antenna A2 is multiplied by k times increases that of the antenna A1. This means that the reception performance of the communication apparatus can be improved rather than increasing the gain by k times. On the other hand, the negative value of the first evaluation function means that the reception performance of the communication apparatus can be improved by increasing the gain of the antenna A1 by k times than by increasing the gain of the antenna A2 by k times. .

  Further, the first evaluation function is a value obtained from the interference power via the antenna A1, the interference power via the antenna A2, and the correlation value between the reception signal of the antenna A1 and the reception signal of the antenna A2. The calculated value of the first evaluation function may be described as an evaluation value. Since the interference power and the correlation value can be measured, the value (evaluation value) of the first evaluation function can be experimentally obtained from the measurable value. Therefore, the communication apparatus determines which gain of the antenna A1 and the antenna A2 greatly affects the reception performance of the communication apparatus based on the value of the first evaluation function obtained using the experimentally obtained value. it can. The communication apparatus improves the reception performance of the communication apparatus by adjusting the impedance of the matching circuit used to adjust the gain of the antenna having the larger influence.

  The communication apparatus can also include a coupling reduction circuit that reduces the correlation value between the reception signal of the antenna A1 and the reception signal of the antenna A2 by reducing the amount of coupling between the antennas A1 and A2. In this case, the communication device also holds the second evaluation function. The second evaluation function is a function that is directly proportional to a value obtained by subtracting SINR (SINR3) when the correlation value between the reception signal of antenna A1 and the reception signal of antenna A2 is multiplied by 1 / k from SINR1. When the second evaluation function takes a positive value, it means that the reception performance can be improved by increasing the gain of the antenna A1 by k times than by increasing the correlation value by 1 / k times. On the other hand, if the second evaluation function takes a negative value, it means that the reception performance can be improved by increasing the correlation value by 1 / k rather than by increasing the gain of the antenna A1 by k. The second evaluation function can also be obtained from values that can be actually measured, such as interference power and correlation values, in the same manner as the first evaluation function.

  As described above, the communication apparatus can specify a circuit having a large influence on the reception performance by using the first evaluation function or the second evaluation function. Here, since neither the first evaluation function nor the second evaluation function includes a value that is not obtained by measurement, the communication apparatus uses an actual measurement value such as interference power or a correlation value to greatly affect reception performance. Can be evaluated for each circuit. Further, the communication apparatus preferentially adjusts a circuit having a large influence on the reception performance so that the reception performance can be improved. For this reason, the communication apparatus can improve reception performance efficiently.

<First Embodiment>
FIG. 2 shows an example of the communication apparatus 10 according to the first embodiment. The communication device 10 includes antennas A1 and A2, matching circuits 12 (12a and 12b), a coupling reduction circuit 13, a matching circuit control unit 21 (21a and 21b), a correlation calculation unit 31, and an interference power calculation unit 32 (32a and 32b). The selection unit 33 is provided. The matching circuit 12 is used to adjust the gain of the antenna. It is assumed that the gain of the antenna A1 is changed by adjusting the impedance of the matching circuit 12a. In addition, it is assumed that the gain of the antenna A2 is changed by adjusting the impedance of the matching circuit 12b. The coupling reduction circuit 13 is used to reduce the coupling amount between the antenna A1 and the antenna A2. In the following description, the power observed through the other antenna when the other antenna receives a signal output from one antenna of the communication apparatus 10 having two antennas is described as combined power. . Note that the amount of coupling is not limited to the coupling power. For example, when a signal transmitted from the antenna A1 is absorbed by another antenna A2, the intensity of the signal observed by the antenna A2 may be referred to as a “coupling amount”. it can.

  The correlation calculation unit 31 calculates a correlation value between the reception signal received by the antenna A1 and the reception signal received by the antenna A2. The correlation calculation unit 31 outputs the calculated correlation value to the selection unit 33. The interference power calculation unit 32a calculates the strength of the interference power received via the antenna A1 from the reception power of the antenna A1 and the strength of the signal S received via the antenna A1. The interference power calculation unit 32b calculates the strength of the interference power received via the antenna A2 from the reception power of the antenna A2 and the strength of the signal S received via the antenna A2. The interference power calculation units 32 a and 32 b both output the calculated interference power intensity to the selection unit 33.

  The selection unit 33 uses the correlation value input from the correlation calculation unit 31, the interference power input from the interference power calculation unit 32a, and the interference power input from the interference power calculation unit 32b, to generate a first evaluation function. Find the value of. Further, the selection unit 33 identifies a circuit having a large influence on SINR out of the matching circuit 12a and the matching circuit 12b based on the calculation result, and selects the identified circuit as a target to be preferentially adjusted. For example, the first evaluation function is a difference between a predicted SINR value (SINR1) when the gain of the antenna A1 is k times and a predicted SINR value (SINR2) when the gain of the antenna A2 is k times. It is a function that is directly proportional. In the following description, k is assumed to be a value larger than 1. When SINR1> SINR2, the selection unit 33 determines that there is a high possibility that the SINR can be improved by changing the gain of the antenna A1, and selects the matching circuit 12a as a circuit to be preferentially processed. On the other hand, when SINR1 <SINR2, the selection unit 33 determines that there is a high possibility that the SINR can be improved by changing the gain of the antenna A2, and selects the matching circuit 12b as a circuit to be preferentially processed. When adjusting the matching circuit 12a, the selection unit 33 requests the matching circuit control unit 21a to increase the gain of the matching circuit 12a. On the other hand, when adjusting the matching circuit 12b, the selection unit 33 requests the matching circuit control unit 21b to increase the gain of the matching circuit 12b.

  The matching circuit control unit 21a measures the power of the signal output from the matching circuit 12a while changing the inductance of the coil and the capacitance of the capacitor of the matching circuit 12a by predetermined values. The matching circuit control unit 21a records the power of the signal output from the matching circuit 12a in association with the amount of change in inductance or capacitance of the capacitor. The matching circuit control unit 21a sets the coil and the capacitor to the conditions when the largest value of the recorded power is obtained. When the value before adjusting the coil and the capacitor is the maximum value of the signal power, the matching circuit control unit 21a notifies the selection unit 33 to that effect. The matching circuit control unit 21b performs the same processing as the matching circuit control unit 21a with the matching circuit 12b as a processing target.

  FIG. 3 shows an example of the hardware configuration of the communication apparatus 10 according to the first embodiment. The communication device 10 includes antennas A1 and A2, matching circuits 12a and 12b, a coupling reduction circuit 13, a radio frequency (RF) circuit 20, a baseband (BB) signal processing circuit 30, and a memory 1. The RF circuit 20 operates as the matching circuit control unit 21a and the matching circuit control unit 21b, and adjusts the circuit selected by the selection unit 33. The RF circuit 20 also performs processing such as modulation and demodulation of signals transmitted and received between the communication apparatus 10 and the base station. The correlation calculation unit 31, the interference power calculation units 32a and 32b, and the selection unit 33 are realized by the baseband signal processing circuit 30. The baseband signal processing circuit 30 further performs baseband signal processing and the like. The memory 1 stores data used for processing of the RF circuit 20 and the baseband signal processing circuit 30.

Next, the SINR calculation formula and the first evaluation function used in the selection unit 33 will be described. First, SINR is expressed as a function of the gain of antenna Ai (i is 1 or 2). Assuming that the received signal of the antenna Ai is v _i and the input signal is s, v _i is expressed as follows.
Here, x _i = G _i H _i and m _i = G _i I _i + N _i . G _i is the gain of the antenna Ai, H _i is a propagation coefficient indicating the state of the propagation path from the base station communicating with the communication apparatus 10 to the antenna Ai, I _i is an external noise received by the antenna Ai, N _i Is the internal noise of the antenna Ai. If the average value of the internal noise is the same between the antennas, and the average value of the external noise is also the same, the following equation holds.
Here, P _I represents external interference power, and P _N represents internal noise power. Therefore, if the matrix Z is (3), it can be expressed as in equation (4) using equations (2a) and (2b).
Furthermore, using Equation (5), if the average power of the input signal s is 1, SINR can be expressed as Equation (6).
In Equation (6), assuming that the correlation of the interference signal between the antennas is equal to the correlation between the antennas of the received signal, SINR can be expressed as Equation (7) as a function of the gain of the antenna and the correlation value r. .

Further, in order to obtain the magnitude relationship between SINR1 and SINR2 using the interference power measured by the communication apparatus 10 and the correlation value, a first evaluation function that is a value proportional to SINR2−SINR1 is derived. The equation for calculating SINR1 is shown in equation (8), and the equation for calculating SINR2 is shown in equation (9). In equations (8) and (9), the square of k is described as a for the sake of easy understanding.
Then, SINR2-SINR1 can be expressed as shown in Equation (10).

Since both SINR1 and SINR2 are positive values, the denominators of Equation (8) and Equation (9) are both positive values. Therefore, a molecule obtained by dividing expression (10) can be expressed as expression (11).
Therefore, the relationship shown in Expression (12) is established.
The interference power between the antenna A1 and the antenna A2 is expressed by Expression (13), and the correlation value between the reception signal of the antenna A1 and the reception signal of the antenna A2 is expressed by Expression (14).
Moreover, k is 1 or more values, because it is ^{a = k 2, (a-} 1) is a positive value. Further, _PN also takes a positive value from the equation (2b). Therefore, since the formulas (12) to (14) and _PN × (a-1) are positive, the relationship of the formula (15) is obtained.

The selection unit 33 uses the right side of Expression (15) as the first evaluation function. Here, the first evaluation function is represented by Y ₁ , Y ₂ , r, P _N , k. Y ₁ is calculated by the interference power calculating section 32a, _{Y 2} is calculated by the interference power calculating unit 32b. r is calculated by the correlation calculation unit 31. K is a constant set arbitrarily. Furthermore, since _PN is the power of internal noise, it is a constant determined according to the communication device 10 and is obtained experimentally. Therefore, if the selection unit 33 holds the value of _PN in advance, the selection unit 33 can obtain the value of the first evaluation function.

When the value of SINR2−SINR1 is positive, the selection unit 33 determines that changing the gain of the antenna A2 is more advantageous for improving SINR. If SINR2−SINR1 = 0, the magnitude of the influence of the gain of the antenna A1 on the SINR and the magnitude of the influence of the gain of the antenna A2 on the SINR are the same. Therefore, when Expression (16) holds, the selection unit 33 requests the matching circuit control unit 21b to adjust the gain of the matching circuit 12b.

On the other hand, when Expression (17) holds, SINR2−SINR1 is negative. For this reason, the selection unit 33 determines that changing the gain of the antenna A1 is more advantageous for improving the SINR, and requests the matching circuit control unit 21a to adjust the gain of the matching circuit 12a.

  Hereinafter, an example of a method of adjusting the matching circuit 12 performed according to the selection result in the selection unit 33 will be described. Here, as an example, Equation (16) holds and the gain of antenna A2 is adjusted. The matching circuit control unit 21b changes the inductance of the variable coil and the capacitance of the variable capacitor included in the matching circuit 12b, and measures the power of the signal output from the matching circuit 12b. Here, in order to make the explanation easy to understand, a case where one variable coil is included as a variable element in the matching circuit 12b is taken as an example.

  The matching circuit control unit 21b adjusts the inductance of the variable coil of the matching circuit 12b within a preset range of change, and the measurement result of the signal power in association with the adjustment is shown in FIG. Can be memorized. In FIG. 4A, the value of the power of the signal output from the matching circuit 12b when the inductance of the variable coil of the matching circuit 12b is changed every 5 nH from the current setting value to −5 nH to +15 nH is adjusted. It is recorded in association with the amount. For example, the signal of the power of Gb0 is output from the matching circuit 12b before adjustment, but if the inductance of the variable coil is reduced by 5 nH, the power of the signal output from the matching circuit 12b becomes Gb1.

  Next, the matching circuit control unit 21b compares the signal power before changing the element setting with the measurement result of the signal power obtained when the element setting is changed, and the signal power is maximized. The matching circuit 12b is adjusted by adopting the setting at that time. For example, in the example shown in FIG. 4A, it is assumed that the signal power becomes Gb2 when the inductance of the variable coil is increased by 5 nH than before the setting of the matching circuit 12b is changed. Furthermore, Gb2 is the maximum value among Gb0 to Gb4. Then, the matching circuit control unit 21b increases the inductance of the coil of the matching circuit 12b by 5 nH, and ends the adjustment. Here, since the matching circuit control unit 21b increases the signal intensity received from the antenna A2 by adjusting the matching circuit 12b, the gain of the antenna A2 is increased.

  On the other hand, as shown in FIG. 4B, even if the matching circuit control unit 21b changes the setting of the matching circuit 12b, the power of the signal output from the matching circuit 12b is determined from the value (Gb0) before the setting change. Suppose that it was not possible to increase it. Then, the matching circuit control unit 21b notifies the selection unit 33 that the signal power cannot be increased by adjusting the matching circuit 12b without changing the setting of the matching circuit 12b. For example, the matching circuit control unit 21b can output a signal indicating that the power of the signal does not increase due to the adjustment of the matching circuit 12b to the selection unit 33.

  When notified from the matching circuit control unit 21b that the adjustment of the matching circuit 12b does not increase the signal power intensity, the selection unit 33 adjusts the matching circuit 12a to the matching circuit control unit 21a. Request. The matching circuit control unit 21a changes the value of the variable coil included in the matching circuit 12a and measures the power of the signal output from the matching circuit 12a by the same procedure as the matching circuit control unit 21b. Here, it is assumed that a result as shown in FIG. Then, the matching circuit control unit 21a increases the inductance of the variable coil by 10 nH in order to set when Ga3 which is the maximum value is obtained. The gain of the antenna A1 is changed by adjusting the matching circuit 12a.

  When Expression (17) is satisfied, the matching circuit control unit 21a changes the setting of the variable element included in the matching circuit 12a in response to a request from the selection unit 33, and sets the voltage of the obtained signal. It is stored in association with the amount of change. For example, the matching circuit control unit 21a can generate the table of FIG. 4C by adjusting the matching circuit 12a. The matching circuit control unit 21a sets the variable element to the setting when the signal voltage is the highest. Further, when the voltage of the signal cannot be increased more than before the setting change, the selection unit 33 is notified in the same manner as the matching circuit control unit 21b. In this case, the matching circuit control unit 21b adjusts the matching circuit 12b in response to a request from the selection unit 33.

  In any of the matching circuit control units 21a and 21b, the adjustment range of the elements included in the matching circuits 12a and 12b is arbitrarily set according to the mounting, and even if the adjustment range is not set. Be good. When the adjustment range is not set, the matching circuit control unit 21a obtains the output of the matching circuit 12a for all values that the variable element can take for the matching circuit 12a, and matches the condition that the output power is maximized. The circuit 12a is set. Similarly, when the adjustment range is not set, the matching circuit control unit 21b similarly adopts the setting when the power of the output signal of the matching circuit 12b is maximized from all the settings that the matching circuit 12b can take. . Furthermore, the matching circuit control unit 21a can change the settings for all the variable elements included in the matching circuit 12a, and the matching circuit control unit 21b can change the settings for all the variable elements in the matching circuit 12b. Shall.

  FIG. 5 is a flowchart for explaining an example of an operation performed in the first embodiment. The selection unit 33 obtains the value of the first evaluation function (step S1). When the calculated value of the first evaluation function is negative, since SINR2−SINR1 is negative, the selection unit 33 determines to prioritize the adjustment of the matching circuit 12a (Yes in step S2). The selection unit 33 requests the matching circuit control unit 21a to adjust the matching circuit 12a. The matching circuit control unit 21a stores the voltage of the signal output from the matching circuit 12a as Va (step S3). Further, the matching circuit control unit 21a changes the impedance of the matching circuit 12a by changing the setting of the variable element included in the matching circuit 12a, and the voltage of the signal output from the matching circuit 12a is maximized. As described above, the setting of the variable element is changed (step S4). The matching circuit control unit 21a determines whether the voltage of the signal output from the matching circuit 12a is higher than Va (step S5). When the voltage of the signal output from the matching circuit 12a is higher than Va, the circuit adjustment ends (Yes in step S5). However, when the voltage of the signal output from the matching circuit 12a is equal to or lower than Va, the matching circuit control unit 21a notifies the selection unit 33 that the adjustment of the matching circuit 12a does not improve the reception performance of the communication device 10. Then, the selection unit 33 requests the matching circuit control unit 21b to adjust the matching circuit 12b. The matching circuit control unit 21b measures the voltage of the signal output from the matching circuit 12b while changing the setting of the variable element of the matching circuit 12b, and sets the matching circuit 12b so that the voltage of the signal of the matching circuit 12b becomes maximum. Adjust (step S6).

  When the calculated value of the first evaluation function is 0 or more, since SINR2−SINR1 is 0 or more, the selection unit 33 decides to give priority to the adjustment of the matching circuit 12b and matches the matching circuit control unit 21b. The adjustment of the circuit 12b is requested (No in step S2). The matching circuit control unit 21b stores the voltage of the signal output from the matching circuit 12b as Vb (step S7). Further, the matching circuit control unit 21b maximizes the voltage of the signal output from the matching circuit 12b by changing the setting of the variable element in the matching circuit 12b (step S8). The matching circuit control unit 21b determines whether the voltage of the signal output from the matching circuit 12b is higher than Vb (step S9). If the voltage of the signal output from the matching circuit 12b is higher than Vb, the circuit adjustment ends (Yes in step S9). When the voltage of the signal output from the matching circuit 12b is Vb or less, the matching circuit control unit 21b notifies the selection unit 33 that the reception performance of the communication device 10 is not improved by the adjustment of the matching circuit 12b. Then, the selection unit 33 requests the matching circuit control unit 21a to adjust the matching circuit 12a. The matching circuit control unit 21a adjusts so that the voltage of the signal output from the matching circuit 12a is maximized by changing the setting of the variable element of the matching circuit 12a (No in step S9, step S10).

  Thus, the communication apparatus 10 can specify which of the matching circuit 12a and the matching circuit 12b has a large influence on the reception performance by using the first evaluation function. In addition, since the first evaluation function does not include a value that is not experimentally obtained, the communication apparatus 10 uses the measured values such as interference power and correlation values to determine the magnitude of the influence on the reception performance for each circuit. Can be evaluated. Further, the communication device 10 preferentially adjusts the identified circuit so that the reception performance can be improved. For this reason, the communication apparatus 10 can improve reception performance efficiently.

<Second Embodiment>
FIG. 6 shows an example of the configuration of the communication device 40 according to the second embodiment. In the second embodiment, a case where a variable element is included in the matching circuit 12a and the coupling reduction circuit 43 will be described as an example. Here, the gain of the antenna A1 may be equal to or greater than the gain of the antenna A2, and the gain of the antenna A1 may be smaller than the gain of the antenna A2.

  The communication device 40 includes a selection unit 41, a coupling reduction circuit control unit 42, a coupling reduction circuit 43, an antenna A1, an antenna A2, a matching circuit 12 (12a, 12b), a matching circuit control unit 21a, a correlation calculation unit 31, and interference power calculation. The unit 32 (32a, 32b) is provided. The operations of the antenna A1, the antenna A2, the matching circuits 12a and 12b, the matching circuit control unit 21a, the correlation calculation unit 31, and the interference power calculation units 32a and 32b are the same as those in the first embodiment. The coupling reduction circuit control unit 42 is realized by the RF circuit 20. The selection unit 41 is assumed to be realized by the BB signal processing circuit 30.

  The coupling reduction circuit 43 includes a variable element, and reduces the coupling amount between the antenna A1 and the antenna A2. The coupling reduction circuit control unit 42 can change the coupling amount of the antenna A1 and the antenna A2 by adjusting the reactance of the coupling reduction circuit 43. When the amount of coupling between antenna A1 and antenna A2 increases, the correlation between the value of the received power received by antenna A1 and the received signal received by antenna A2 increases. Therefore, the coupling reduction circuit control unit 42 changes the setting of the variable element included in the coupling reduction circuit 43 so that the correlation value becomes small in response to a request from the selection unit 41.

  The selection unit 41 uses the correlation value input from the correlation calculation unit 31, the interference power input from the interference power calculation unit 32a, and the interference power input from the interference power calculation unit 32b to use the second evaluation function. Find the value of. The second evaluation function is a predicted value of SINR (SINR1) when the gain of antenna A1 is multiplied by k, and a predicted value of SINR when the correlation value of the received signals of antennas A1 and A2 is multiplied by 1 / k. It is a function that is directly proportional to the difference of (SINR3). In the following description, k is assumed to be a value larger than 1. A method for deriving the second evaluation function and a specific example will be described later. When the value of the second evaluation function indicates that SINR1> SINR3, the selection unit 41 determines that there is a high possibility that the reception performance can be improved by changing the gain of the antenna A1, and sets the matching circuit 12a. Select as a circuit to preferentially adjust. On the other hand, when the value of the evaluation function means that SINR1 <SINR3, the selection unit 41 determines that there is a high possibility that the reception performance can be improved by reducing the correlation value, and the coupling reduction circuit 43 is given priority. Select the circuit to be adjusted.

  When the selection unit 41 selects the matching circuit 12a as a circuit to be preferentially adjusted, the selection unit 41 requests the matching circuit control unit 21a to increase the gain of the matching circuit 12a. On the other hand, when the coupling reduction circuit 43 is selected as a target to be preferentially adjusted, the selection unit 41 reduces the coupling amount of the antenna A1 and the antenna A2 by the coupling reduction circuit 43 with respect to the coupling reduction circuit control unit 42b. Request.

Next, a method for deriving the second evaluation function used in the selection unit 41 and a specific example of the second evaluation function will be described. SINR1 is as shown in Equation (8) described above. SINR3 can be expressed by the following equation from equation (7). In the following, the square of k is described as a in the calculation formula as appropriate.

Therefore, Expression (19) is obtained from Expression (8) and Expression (18).

Since both SINR1 and SINR3 are positive values, the denominators of Equation (8) and Equation (18) are both positive values. Therefore, the molecule A obtained by dividing the equation (19) can be expressed as the equation (20).
Further transformation of equation (20) yields:
Here, since k is larger than 1 and a = k ² , (a−1) is a positive value. Further, the square of the absolute value of the gain of the antenna A1 is also a positive value. Furthermore, it can be said that _PN also takes a positive value from the equation (2b). Therefore, Expression (22) is obtained from Expression (21).
Substituting equation (13) into equation (22) yields equation (23).

The selection unit 41 uses the right side of Expression (23) as the second evaluation function. Here, _{Y 1} is calculated by the interference power calculating section 32a, _{Y 2} is calculated by the interference power calculating unit 32b. r is calculated by the correlation calculation unit 31. K is a constant set arbitrarily. Furthermore, since _PN is the power of internal noise, it is a constant determined for each communication device 40 and is obtained experimentally. Therefore, if the selection unit 41 holds the value of _PN in advance, the value of the second evaluation function can be obtained.

When SINR1-SINR3 is positive, the selection unit 41 determines that increasing the gain of the antenna A1 is more advantageous for improving SINR than decreasing the correlation value. In addition, when SINR1−SINR3 = 0, the magnitude of the effect of adjusting the gain of antenna A1 to k times on SINR and the magnitude of the effect of adjusting the correlation value to 1 / k times on SINR. Can be predicted to be the same. Therefore, when Expression (24) holds, the selection unit 41 requests the matching circuit control unit 21a to adjust the gain of the matching circuit 12a.

On the other hand, when Expression (25) is satisfied, SINR1−SINR3 is negative. For this reason, the selection unit 41 determines that the SINR can be improved more easily by reducing the correlation value than by increasing the gain of the antenna A1, and the coupling amount of the coupling reduction circuit 43 is determined by the coupling reduction circuit control unit 42. Requires adjustments to decrease.

  The processing performed by the matching circuit control unit 21a when Expression (24) is satisfied and the gain of the antenna A1 is adjusted is the same as that when Expression (17) is satisfied in the first embodiment. When the matching circuit control unit 21a notifies that the voltage of the output signal of the matching circuit 12a cannot be increased, the selection unit 41 requests the coupling reduction circuit control unit 42 to adjust the coupling reduction circuit 43. The coupling reduction circuit control unit 42 uses the variable element included in the coupling reduction circuit 43 to change the impedance of the coupling reduction circuit 43, and calculates the correlation value between the reception signals of the antennas A 1 and A 2 from the correlation calculation unit 31. get. The coupling reduction circuit control unit 42 records the obtained correlation value as shown in FIG. 7 in association with the setting of the variable element. Although the example of FIG. 7 shows an example in which the capacity of one variable capacitor is changed, the coupling reduction circuit 43 can include a variable coil, and both the variable capacitor and the variable coil can be provided. It can also be provided. In addition, the number of variable coils and the number of variable capacitors adjusted by the coupling reduction circuit control unit 42 are arbitrarily changed according to mounting. The coupling reduction circuit control unit 42 sets each variable element included in the coupling reduction circuit 43 to a value when the correlation value becomes the smallest. For example, in the example of FIG. 7, since Cor2 is the minimum correlation value, the coupling reduction circuit control unit 42 reduces the capacitance of the variable capacitor of the coupling reduction circuit 43 by 0.5 pF.

  Even when Expression (25) is satisfied, the coupling reduction circuit control unit 42 changes the setting of the variable element included in the coupling reduction circuit 43 in response to a request from the selection unit 41, and correlates the obtained signals. The value is stored in association with the change amount of the setting. The coupling reduction circuit control unit 42 sets the variable element to the setting when the signal voltage is the highest. Further, when the voltage of the signal cannot be made larger than before the setting change, the selection unit 41 is notified in the same manner as the matching circuit control unit 21a. In this case, the matching circuit control unit 21a adjusts the matching circuit 12a in response to a request from the selection unit 41.

  FIG. 8 is a flowchart for explaining an example of an operation performed in the second embodiment. The selection unit 41 obtains the value of the second evaluation function (step S21). When the calculated value of the second evaluation function is 0 or more, since SINR1−SINR3 is 0 or more, the selection unit 33 determines to prioritize the adjustment of the matching circuit 12a (Yes in Step S22). The processes of steps S23 to S25 are the same as steps S3 to S5 described with reference to FIG. If the voltage of the signal output from the matching circuit 12a in step S25 is Va or less, the matching circuit control unit 21a notifies the selection unit 41 that the adjustment of the matching circuit 12a does not improve the reception performance of the communication device 40 (step S25). No in S25). Then, the selection unit 41 requests the coupling reduction circuit control unit 42 to adjust the coupling reduction circuit 43. The coupling reduction circuit control unit 42 adjusts the coupling reduction circuit 43 so that the correlation value between the reception signal of the antenna A1 and the reception signal of the antenna A2 is minimized (step S26).

  When the calculated value of the second evaluation function is negative, since SINR1-SINR3 is negative, the selection unit 41 determines to prioritize adjustment of the coupling reduction circuit 43 and couples to the coupling reduction circuit control unit 42. The adjustment of the reduction circuit 43 is requested (No in step S22). The coupling reduction circuit control unit 42 stores the correlation value before adjustment of the coupling reduction circuit 43 as Cor0 (step S27). Further, the coupling reduction circuit control unit 42 minimizes the correlation value between the reception signal of the antenna A1 and the reception signal of the antenna A2 by changing the setting of the variable element in the coupling reduction circuit 43 (step S28). The coupling reduction circuit control unit 42 determines whether the correlation value is lower than Cor0 (step S29). If the correlation value is lower than Cor0, the circuit adjustment ends (Yes in step S29). When the correlation value is greater than or equal to Cor0, the coupling reduction circuit control unit 42 notifies the selection unit 41 that the reception performance of the communication device 10 is not improved by the adjustment of the coupling reduction circuit 43. Then, the selection unit 41 requests the matching circuit control unit 21a to adjust the matching circuit 12a. The matching circuit control unit 21a adjusts the voltage of the signal output from the matching circuit 12a to be maximum by changing the setting of the variable element of the matching circuit 12a (No in step S29, step S30).

  As described above, the communication device 40 can specify which of the matching circuit 12a and the coupling reduction circuit 43 has a large influence on the reception performance by using the second evaluation function. In addition, since the second evaluation function does not include a value that is not experimentally obtained, the communication device 40 uses the measured values such as the interference power and the correlation value to determine the magnitude of the influence on the reception performance for each circuit. Can be evaluated. The communication device 40 can improve the reception performance efficiently by preferentially adjusting a circuit having a large influence on the reception performance.

<Third Embodiment>
FIG. 9 shows an example of the configuration of the communication device 50 according to the third embodiment. In the third embodiment, a case where a variable element is included in the matching circuit 12a, the matching circuit 12b, and the coupling reduction circuit 43 will be described as an example. The communication device 50 is assumed to improve the reception performance by adjusting the matching circuit 12a, the matching circuit 12b, and the coupling reduction circuit 43.

  The communication device 50 includes a selection unit 51, an antenna A1, an antenna A2, a matching circuit 12 (12a, 12b), a matching circuit control unit 21 (21a, 21b), a correlation calculation unit 31, and an interference power calculation unit 32 (32a, 32b). The coupling reduction circuit control unit 42 and the coupling reduction circuit 43 are provided. The operations of the antenna A1, the antenna A2, the matching circuits 12a and 12b, the matching circuit control units 21a and 21b, the correlation calculation unit 31, and the interference power calculation units 32a and 32b are the same as those in the first or second embodiment. The operations of the coupling reduction circuit control unit 42 and the coupling reduction circuit 43 are the same as those in the second embodiment. The selection unit 51 is assumed to be realized by the BB signal processing circuit 30.

The selection unit 51 holds the first to third evaluation functions. The selection unit 51 determines the order of priority adjustment for the matching circuit 12a, the matching circuit 12b, and the coupling reduction circuit 43 according to the values of the first to third evaluation functions. The first evaluation function is the right side of equation (15), and the second evaluation function is the right side of equation (23). Further, the third evaluation function includes SINR (SINR2) when the gain of the antenna A2 is multiplied by k, and SINR (SINR3) when the correlation value of the received signals of the antenna A1 and the antenna A2 is multiplied by 1 / k. This function is directly proportional to the difference between the two and is represented by the right side of the equation (26). Note that the third evaluation function is derived by performing calculation by replacing SINR1 with SINR2 in the second evaluation function derivation method. In the following description, k is a value of 1 or more.

  Each of the first to third evaluation functions uses the correlation value input from the correlation calculation unit 31, the interference power input from the interference power calculation unit 32a, and the interference power input from the interference power calculation unit 32b. Can be calculated.

  FIG. 10 is a flowchart illustrating an example of determination performed by the selection unit 51. FIG. 10 shows an example of processing. For example, the determination performed first may be determination using any of the first to third evaluation functions.

  The selection unit 51 calculates the value (E) of the first evaluation function and determines whether the obtained value is 0 or more (steps S41 and S42). When the value of the first evaluation function is negative, since the reception performance is improved when the gain of the antenna A1 is increased by k times than when the gain of the antenna A2 is increased by k times, the selection unit 51 sets the matching circuit 12a to The adjustment is performed with priority over the matching circuit 12b (No in step S42). Then, the selection unit 51 calculates the value (F1) of the second evaluation function and determines whether the obtained value is 0 or more (steps S43 and S44). When the value of the second evaluation function is negative, even if the gain of the antenna A1 is increased by k, the reception performance is not improved as compared with the case where the correlation value is increased by 1 / k. The adjustment of 43 is given priority over the adjustment of the matching circuit 12a. Therefore, the selection unit 51 determines to perform adjustment in the order of the coupling reduction circuit 43, the matching circuit 12a, and the matching circuit 12b (No in step S44, S45).

  On the other hand, when the value of the second evaluation function is 0 or more in step S44, the selection unit 51 gives the highest priority to the adjustment of the matching circuit 12a among the matching circuit 12a, the matching circuit 12b, and the coupling reduction circuit 43 ( Yes in step S44). Therefore, in order to determine which of the coupling reduction circuit 43 and the matching circuit 12b the circuit to be preferentially adjusted next to the matching circuit 12a, the selection unit 51 sets the value (F2) of the third evaluation function. Is calculated (step S46). When the value (F2) of the third evaluation function is positive, if the gain of the antenna A2 is increased by k times, the reception performance is improved as compared with the case where the correlation value is increased by 1 / k times. For this reason, the selection unit 51 prioritizes the adjustment of the matching circuit 12b over the adjustment of the coupling reduction circuit 43 when the value of F2 is 0 or more. Therefore, the selection unit 51 determines to perform adjustment in the order of the matching circuit 12a, the matching circuit 12b, and the coupling reduction circuit 43 (Yes in step S47, S48). When the value (F2) of the third evaluation function is negative, the selection unit 51 prioritizes the adjustment of the coupling reduction circuit 43 over the adjustment of the matching circuit 12b. For this reason, the selection unit 51 determines to perform adjustment in the order of the matching circuit 12a, the coupling reduction circuit 43, and the matching circuit 12b (No in step S47, S49).

  When the value of the first evaluation function is positive, even if the gain of the antenna A1 is increased by k, the reception performance is not improved as compared with the case where the gain of the antenna A2 is increased by k. For this reason, when the value of the first evaluation function is 0 or more, the selection unit 51 prioritizes the adjustment of the matching circuit 12b over the adjustment of the matching circuit 12a (Yes in step S42). Next, the selection unit 51 calculates a third evaluation function (F2) in order to determine which of the coupling reduction circuit 43 and the matching circuit 12b is preferentially adjusted (step S50). When the value of the third evaluation function (F2) is negative, if the correlation value is increased by 1 / k times, the reception performance is improved as compared to the gain of the antenna A2 being increased by k times. The adjustment of the coupling reduction circuit 43 is given priority over the adjustment of the matching circuit 12b. Accordingly, the selection unit 51 determines to perform adjustment in the order of the coupling reduction circuit 43, the matching circuit 12b, and the matching circuit 12a (No in step S51, S52).

  On the other hand, when the value of the third evaluation function is 0 or more in step S51, the selection unit 51 gives the highest priority to the adjustment of the matching circuit 12b among the matching circuit 12a, the matching circuit 12b, and the coupling reduction circuit 43 ( Yes in step S51). Therefore, in order to determine a circuit to be preferentially adjusted after the matching circuit 12b, the selection unit 51 calculates the value (F1) of the second evaluation function (step S53). When the value of the second evaluation function is positive, if the gain of the antenna A1 is multiplied by k, the reception performance is improved as compared with increasing the correlation value by 1 / k. For this reason, the selection unit 51 prioritizes the adjustment of the matching circuit 12a over the adjustment of the coupling reduction circuit 43 when F1 is 0 or more. Accordingly, the selection unit 51 determines to perform adjustment in the order of the matching circuit 12b, the matching circuit 12a, and the coupling reduction circuit 43 (Yes in step S54, S56). On the other hand, when the value of the second evaluation function is negative, if the correlation value is increased by 1 / k, the reception performance is improved as compared with the gain of the antenna A1 being multiplied by k. The adjustment of the circuit 43 is prioritized over the adjustment of the matching circuit 12a. Therefore, the selection unit 51 determines to perform adjustment in the order of the matching circuit 12b, the coupling reduction circuit 43, and the matching circuit 12a (No in step S54, S55).

  The selection unit 51 first requests the adjustment of the circuit with the highest priority in order to adjust the circuits in the descending order of priority. When notified that the adjustment of the circuit with the highest priority is completed, the selection unit 51 requests the adjustment of the circuit having the second highest priority. After being notified that the adjustment of the second priority circuit has been completed, the selection unit 51 requests the adjustment of the third priority circuit. When the adjustment of all the circuits is completed, the selection unit 51 ends the process.

  For example, it is assumed that the priority order is the order of the matching circuit 12a, the matching circuit 12b, and the coupling reduction circuit 43 as in step S48 of FIG. At this time, the selection unit 51 first requests the matching circuit control unit 21a to adjust the matching circuit 12a. As described in the first and second embodiments, the matching circuit control unit 21a adjusts the variable element included in the matching circuit 12a, thereby increasing the power of the signal output from the matching circuit 12a to the maximum value. To. If the signal power becomes maximum when the setting of the matching circuit 12a is not changed, the matching circuit control unit 21a does not change the setting of the variable element of the matching circuit 12a. When the adjustment is completed, the matching circuit control unit 21a notifies the selection unit 51 of the completion of the adjustment. Upon receiving the notification from the matching circuit control unit 21a, the selection unit 51 requests the matching circuit control unit 21b to adjust the matching circuit 12b. The matching circuit control unit 21b adjusts the matching circuit 12b by the same processing as the matching circuit control unit 21a. When the adjustment is completed, the matching circuit control unit 21b notifies the selection unit 51 of the completion of the adjustment. Upon receiving the notification from the matching circuit control unit 21b, the selection unit 51 requests the coupling reduction circuit control unit 42 to adjust the coupling reduction circuit 43. The coupling reduction circuit control unit 42 changes the setting of the variable element included in the coupling reduction circuit 43 by the same processing as the procedure described in the second embodiment, and minimizes the correlation value. When the adjustment is completed, the coupling reduction circuit control unit 42 notifies the selection unit 51 of the completion of the adjustment. When the selection unit 51 recognizes that the processing has been completed for all the circuits to be processed, the selection unit 51 ends the processing.

  According to the third embodiment, processing priorities of a plurality of circuits can be determined based on values obtained by substituting actually measurable values into the first to third evaluation functions. For this reason, the communication apparatus 50 can improve reception performance efficiently.

<Fourth Embodiment>
In the fourth embodiment, a modified example of the adjustment method in the communication device 50 in which the matching circuit 12a, the matching circuit 12b, and the coupling reduction circuit 43 include variable elements will be described. The communication device 50 specifies a combination of circuits to be adjusted according to the values of the first to third evaluation functions.

  FIG. 11 is a flowchart for explaining an example of the operation of the selection unit 51 in the fourth embodiment. In the example of FIG. 11, it is assumed that the selection unit 51 stores a threshold value T1. The threshold T1 is arbitrarily set according to the implementation. Also, FIG. 11 is an example, and for example, the order of determination in steps S62 and S64 may be changed. Furthermore, in order to select a circuit to be adjusted, the second evaluation function may be used.

  The selection unit 51 obtains the value (E) of the first evaluation function, and determines whether the obtained value is −T1 or less (steps S61 and S62). When the value of the first evaluation function is −T1 or less, the selection unit 51 selects the matching circuit 12a as a control target, and determines that the matching circuit 12b and the coupling reduction circuit 43 are not adjusted (Yes in step S62). Step S63). On the other hand, when the value of the first evaluation function is greater than -T1, the selection unit 51 determines whether the value of the first evaluation function is greater than T1 (step S64). When the value of the first evaluation function is larger than T1, the selection unit 51 selects the matching circuit 12b as a control target, and determines that the matching circuit 12a and the coupling reduction circuit 43 are not adjusted (Yes in step S64, step S65).

  When the value of the first evaluation function is greater than −T1 but less than or equal to T1, the selection unit 51 has an extremely large influence on the reception performance of the communication device 50 in both the matching circuit 12a and the matching circuit 12b. Judge that there is no. Therefore, the selection unit 51 further calculates a third evaluation function, and compares the obtained value with -T1 (No in step S64, steps S66, S67). When the value of the third evaluation function is less than −T1, the selection unit 51 determines that the influence of the coupling reduction circuit 43 on the reception performance is large. Therefore, the selection unit 51 selects the coupling reduction circuit 43 as a control target, and determines not to adjust the matching circuit 12a and the matching circuit 12b (Yes in Step S67, Step S68). On the other hand, when the value of the third evaluation function is −T1 or more, the selection unit 51 determines that the influence of any circuit on reception performance is not extremely large compared to other circuits. Therefore, the selection unit 51 selects all of the matching circuit 12a, the matching circuit 12b, and the coupling reduction circuit 43 as control targets (No in step S67, step S69).

  The selection unit 51 requests the matching circuit control unit 21a, the matching circuit control unit 21b, and the coupling reduction circuit control unit 42 to adjust the circuit according to the combination of the circuits selected as the control targets. The operations of the matching circuit control unit 21a, the matching circuit control unit 21b, and the coupling reduction circuit control unit 42 are the same as those in the third embodiment. When the selection unit 51 recognizes that all the circuits selected as adjustment targets have been adjusted, the selection unit 51 ends the process.

  In this way, the number of circuits to be adjusted can be reduced by selecting combinations of circuits that have a large influence on reception performance using the evaluation function. When the number of circuits to be adjusted decreases, the time required for adjustment and the amount of processing decrease, so that the reception performance of the communication device 50 is efficiently improved.

<Fifth Embodiment>
In the fifth embodiment, a description will be given of a communication device 50 that selects a circuit to be adjusted using an empirical formula representing a transmission characteristic of MIMO when performing MIMO reception. In the fifth embodiment, the interference power calculation units 32a and 32b also calculate the value of the signal power. That is, the interference power calculation unit 32a also calculates the power of the signal received via the antenna A1. Similarly, the interference power calculation unit 32b also calculates the power of the signal received via the antenna A2. When the interference power calculation unit 32 calculates the signal power, the calculation of Expression (27) is performed.

The interference power calculation units 32 a and 32 b output the signal power value to the selection unit 51. The selector 51 obtains the gain ratio B using the value of the signal power. Formula (28) shows the formula for calculating the gain ratio B.
Further, it is assumed that the selection unit 51 calculates the gain difference X from Expression (29) using the value of the gain ratio.

Next, an empirical formula representing the transmission characteristics of MIMO will be described. FIG. 12 is a diagram illustrating examples of eigenvalues and transmission characteristics of MIMO. When the base station transmits data to the communication device 50 using two antennas, the propagation path matrix is as shown in Expression (30), and the propagation path is expressed as shown in FIG. .
It is assumed that the first eigenvalue (λ ₁ ) and the second eigenvalue (λ ₂ ) are obtained from the propagation path matrix of Expression (30) as shown in FIG. In this case, since the total power of the propagation path coefficient does not change, the total power of the propagation path coefficient is the total power of the path represented by two eigenvalues as shown in Expression (31).

When the propagation path matrix is expressed by Equation (30), the MIMO channel capacity C is expressed by Equation (32). In the equation (32), S / N is SINR.
From equation (32), it can be said that the transmission capacity takes a large value when the values of the first eigenvalue and the second eigenvalue are equal, but the transmission capacity decreases as the difference between the two eigenvalues increases.

  FIG. 13 shows an example of the relationship between the magnitude of the first eigenvalue and the correlation value of the received signal between the antennas. FIG. 13 is a simulation result of the relationship between the first eigenvalue and the correlation value when the average total power of the propagation path is 4 in the Rayleigh fading environment. As shown in FIG. 13, when the correlation value of the received signal between the antennas is large, the average power of the first eigenvalue is large. As shown in Equation (31), the total power of the propagation path is constant, so that the second eigenvalue decreases as the average power of the first eigenvalue increases. Since the horizontal axis in FIG. 13 is the square value of the correlation value between the antennas, it can be seen from FIG. 13 that the average power of the first eigenvalue is proportional to the square of the correlation value. FIG. 13 shows a simulation result when the gains between the antennas are different. In the legend of FIG. 13, the letter E and the number following the letter E represent a multiplier of 10. For example, -2.00E + 01 represents -20.

FIG. 14 shows an example of the relationship between the magnitude of the first eigenvalue and the gain difference between the antennas. FIG. 14 is also a simulation result when the average total power of the propagation path is 4 in the Rayleigh fading environment. The horizontal axis of FIG. 14 is a function G of the gain difference X between antennas shown in Expression (33).
In order to make the relationship between the values G and X on the horizontal axis in FIG. 14 easier to understand, the value of X used to calculate the value of G is also shown on the horizontal axis. As the gain difference between the antennas increases, the average power value of the first eigenvalue increases. Further, the average power of the first eigenvalue varies linearly with respect to the value of G. FIG. 14 shows simulation results when the correlation values of the received signals between the antennas have various values.

Using FIG. 13 and FIG. 14, the average power value Z of the first eigenvalue of MIMO when the average total power of the propagation path is 4 can be expressed by Expression (34). Hereinafter, Expression (34) may be described as a characteristic function.

  As described above, when the difference between the first eigenvalue and the second eigenvalue increases, the channel capacity decreases and communication efficiency tends to deteriorate. Therefore, the larger the average power of the first eigenvalue, the larger the circuit adjustment amount for improving the communication efficiency. Further, since the reception characteristic is required to be greatly improved as the average power of the first eigenvalue increases, it is also desirable that the number of circuits to be adjusted increases. Therefore, the selection unit 51 obtains the value of the first eigenvalue using the characteristic function before adjusting the circuit. When the first eigenvalue is equal to or greater than the threshold value, the selection unit 51 sets the matching circuit 12a, the matching circuit 12b, and the coupling reduction circuit 43. Decide to adjust everything. On the other hand, if the value of the first eigenvalue is less than the threshold value, the selection unit 51 determines that some of the matching circuit 12a, the matching circuit 12b, and the coupling reduction circuit 43 are to be adjusted. For example, when the value of the first eigenvalue is equal to or smaller than the threshold value, the selection unit 51 can set the matching circuit 12a and the matching circuit 12b as adjustment targets. Here, the selection unit 51 can use, as the threshold value, the value of the first eigenvalue at which MIMO channel capacity is likely to deteriorate.

  FIG. 15 is an example of the relationship between MIMO channel capacity and SINR. An example of how to obtain the threshold will be described with reference to FIG. FIG. 15 is a result of simulating channel capacity by varying the SINR value in the case where the first eigenvalue takes various values. 15 also simulates the case where the average total power of the propagation path is 4 in the Rayleigh fading environment. From the result of FIG. 15, it can be said that even if the value of the first eigenvalue is changed from 3.5 to 3.7, the degradation of the channel capacity is not remarkable. However, when the value of the first eigenvalue exceeds 3.7, the channel capacity is greatly deteriorated. Therefore, for example, the threshold value can be set to a value between 3.5 and 4 using the simulation result of FIG.

  FIG. 16 is a flowchart for explaining an example of the operation of the selection unit 51 in the fifth embodiment. The selection unit 51 obtains the value of the characteristic function Z using the gain difference X and the correlation value r, and compares the obtained value with a threshold value stored in advance (step S81). Here, it is assumed that the gain difference is calculated by the selection unit 51 using the gain of each antenna and the equations (28) and (29). When the value of the characteristic function is less than the threshold value, the selection unit 51 selects the matching circuit 12a and the matching circuit 12b as circuits to be adjusted (No in step S81, step S82). Further, the selection unit 51 obtains the value of the first evaluation function, and when the value E of the first evaluation function is 0 or more, selects the matching circuit 12b as a circuit to be preferentially adjusted (steps S83 and S84). Yes, step S85). On the other hand, when the value E of the first evaluation function is negative, the selection unit 51 selects the matching circuit 12a as a circuit to be preferentially adjusted (step S83, No in step S84, step S86). When the value of the characteristic function is equal to or greater than the threshold value, the selection unit 51 selects the matching circuit 12a, the matching circuit 12b, and the coupling reduction circuit 43 as the adjustment target circuits (Yes in Step S81, Step S87). Then, the selection unit 51 determines the priority of adjustment for the matching circuit 12a, the matching circuit 12b, and the coupling reduction circuit 43 using the first to third evaluation functions (step S88). The procedure of step S88 is the same as the procedure described with reference to FIG.

  As described above, when MIMO communication is performed in the communication device 50, the adjustment target circuit is selected after the reception characteristic adjustment amount is predicted according to the channel capacity. Is selected. Furthermore, in the communication device 50, the priority order among the selected circuits to be adjusted is determined based on the first to third evaluation functions. This means that a circuit having a large influence on the reception characteristic is specified by a value experimentally obtained in the communication device 50, and a circuit having a large influence on the reception characteristic can be preferentially adjusted.

<Others>
The present invention is not limited to the above-described embodiment, and can be variously modified. Some examples are described below.

  The methods according to the first to fourth embodiments are not only used when MIMO communication is performed in the communication devices 10, 40, and 50, but also when any communication using a plurality of antennas such as diversity is performed. Applicable.

  In any embodiment, when the value of the first evaluation function becomes 0, the matching circuit 12a may be set to be adjusted. Similarly, when the value of the second or third evaluation function is 0, the coupling reduction circuit 43 may be adjusted.

  In the above example, the matching circuit control units 21a and 21b and the coupling reduction circuit control unit 42 adjust the circuit for all cases where the variable elements included in the control target circuit take values within a certain adjustment range. Adjustments are made based on the results. However, this is an example, and adjustment may be performed by other methods. For example, it is assumed that the matching circuit 12a includes a variable capacitor whose capacitance can be changed by ΔC. The matching circuit control unit 21a measures the voltage of the output signal from the matching circuit 12a while changing the capacity of the variable capacitor by 5ΔC. When the voltage of the output signal increases, the matching circuit control unit 21a determines the amount of change in the capacity of the variable capacitor. The output signal can be measured while being reduced. Similarly, the matching circuit control unit 21b and the coupling reduction circuit control unit 42 observe whether the effect of the change is obtained by changing the variable element included in the control target circuit with a predetermined width, and the desired effect is obtained. The variable element can be finely adjusted for the area.

FIG. 17 is a flowchart illustrating a modified example of the operation of the matching circuit control unit. In the example of FIG. 17, when the matching circuit control unit 21 receives an adjustment request from the selection unit 33, the matching circuit control unit 21 compares the currently set value with a value one step larger or one step smaller than the current set value. Based on the result, decide whether to change the setting. For example, it is assumed that the capacitances that can be set in the variable capacitors included in the matching circuit 12 are discontinuous n values c ₁ , c ₂ ,..., C _n . In FIG. 17, m is a value from 1 to n. When the communication device 10 is powered on, the matching circuit control unit 21 sets m = 1, thereby setting the capacitance of the variable capacitor included in the matching circuit 12 to c1 (step S91). Upon receiving a request for adjustment from the selector 33, the matching circuit control unit 21 measures the power p _m of the current output from the matching circuit 12 (step S92). Thereafter, the matching circuit control unit 21 determines whether m is less than n (step S93). If m is less than n, the matching circuit control unit 21 sets the set value of the variable capacitor in one step larger value _{c m + 1,} measuring the output _{p m + 1} from the matching circuit 12 (Yes in step S93, step S94 , S95). If the power _{p m} is _{p m + 1} is smaller than, the matching circuit control unit 21, the value of the variable capacitor and the value of the adjusted increments one value of m (Yes in step S96, step S97). If the power _{p m} is _{p m + 1} or more, matching circuit control unit 21 returns to the value before adjusting the value of the variable capacitor (No in step S96, step S98). After the processing of step S97 or S98, the matching circuit control unit 21 waits until a new adjustment is requested from the selection unit 33.

When m is n, the matching circuit control unit 21 sets the setting value of the variable capacitor to a value c _m−1 that is smaller by one step, and measures the output p _m−1 from the matching circuit 12 (in step S93). No, steps S99, S100). If the power _{p m} is _{p m-1} less than, the matching circuit control unit 21, the value of the variable capacitor and the value after adjustment, one decrements the value of m (Yes in step S101, step S102). When the power p _m is equal to or higher than p _m−1 , the matching circuit control unit 21 returns the value of the variable capacitor to the value before adjustment (No in step S101, step S103). Even after the processing of step S102 or S103, the matching circuit control unit 21 stands by until a new adjustment is requested from the selection unit 33.

  Note that FIG. 17 illustrates the case of the communication device 10 as an example, but the processing illustrated in FIG. 17 may be performed by the communication device 40 or the communication device 50. Further, in the communication device 40 and the communication device 50, the coupling reduction circuit control unit 42 can adjust the variable capacitor included in the coupling reduction circuit 43 by using the same method as in FIG. FIG. 17 shows an example in which the adjustment target is a variable capacitor, but the same processing may be performed when the adjustment target is a variable coil.

DESCRIPTION OF SYMBOLS 1 Memory 10, 40, 50 Communication apparatus 12 Matching circuit 13 Coupling reduction circuit 20 RF circuit 21 Matching circuit control part 30 BB signal processing circuit 31 Correlation calculation part 32 Interference power calculation part 33, 41, 51 Selection part 42 Coupling reduction circuit control Part 43 Coupling reduction circuit

Claims (8)

A first antenna;
A second antenna;
A first adjustment circuit for adjusting the gain of the first antenna;
A second adjustment circuit for adjusting the gain of the second antenna;
A first interference power calculator that calculates first interference power received from the first antenna;
A second interference power calculation unit for calculating second interference power received from the second antenna;
A correlation calculation unit for calculating a correlation value between the reception signal of the first antenna and the reception signal of the second antenna;
More than the influence of the gain of the first antenna on the reception performance calculated using the first interference power, the second interference power, and the correlation value, and the reception performance via the first and second antennas A selection unit that selects an adjustment circuit having a larger influence on the reception performance by using an evaluation value that takes a positive value when the influence of the gain of the second antenna on the reception performance is large;
A communication apparatus comprising: a circuit control unit that preferentially adjusts the selected adjustment circuit so that the reception performance is improved. A coupling reduction circuit for reducing the correlation value by reducing the amount of coupling between the first antenna and the second antenna;
The selection unit includes:
The influence of the gain of the first antenna on the reception performance is expressed by using the first interference power, the second interference power, and the correlation value, and the influence of the correlation value on the reception performance. Using an evaluation function that takes a positive value if greater than, determining which of the gain of the first antenna and the correlation value has a greater effect on the reception performance;
If it is determined that the correlation value has a greater influence on the reception performance than the gain of the first antenna, the coupling reduction circuit is selected as a circuit for preferential adjustment,
The communication device according to claim 1, wherein the circuit control unit prioritizes adjustment of the coupling reduction circuit over adjustment of the first and second adjustment circuits. The selection unit uses the evaluation value and the evaluation function to determine the order of the influence on the reception performance with respect to the gain of the first antenna, the gain of the second antenna, and the correlation value. And select the combination of circuits that will be used to adjust the value that has a relatively large impact,
The communication apparatus according to claim 2 , wherein the circuit control unit adjusts a circuit included in the selected combination so that the reception performance is improved. The selection unit is configured to receive the received signal obtained from the first and second antennas when the gain of the first antenna is changed to a product of the gain of the first antenna and a predetermined numerical value, A first signal-to-noise interference ratio, which is a ratio of noise received from the first and second antennas and a total value of interference power, is multiplied by the product of the gain of the second antenna and the predetermined numerical value. The ratio between the received signal obtained from the first and second antennas and the total value of the noise and interference power received from the first and second antennas when the gain of the antenna is changed The communication apparatus according to claim 2 or 3 , wherein a function that is directly proportional to a value subtracted from a certain second signal-to-noise interference ratio is used for calculation of the evaluation value. The selection unit obtains from the first and second antennas when the correlation value is changed from the first signal-to-noise interference ratio to a value obtained by dividing the correlation value by the predetermined numerical value. A function that is directly proportional to the magnitude of the received signal and the value obtained by subtracting the third signal-to-noise interference ratio, which is the ratio of the noise received from the first and second antennas to the total value of the interference power, The communication device according to claim 4, wherein the communication device is used as the evaluation function. The selection unit, when MIMO communication using the first and second antennas are performed, a gain difference that is a difference between the gain of the first antenna and the gain of the second antenna; expressed as a function of the correlation value, thereby calculating the value of the characteristic function in which the receiver performance is better small value, the calculated values of the characteristic function is compared with a threshold value,
When the calculated value is smaller than the threshold value, the selection unit selects the first adjustment circuit and the second adjustment circuit as adjustment targets, and uses the evaluation value to select the first adjustment circuit. 6. The communication device according to claim 1, wherein an adjustment circuit to be preferentially adjusted is selected from the second adjustment circuit and the second adjustment circuit. The selection unit, when MIMO communication using the first and second antennas are performed, a gain difference that is a difference between the gain of the first antenna and the gain of the second antenna; Expressed as a function of the correlation value, the value of the characteristic function that becomes a smaller value as the reception performance is better, and the calculated value of the characteristic function is compared with a threshold value,
When the calculated value is smaller than the threshold value, the selection unit selects the first adjustment circuit and the second adjustment circuit as adjustment targets, and uses the evaluation value to select the first adjustment circuit. And an adjustment circuit to be preferentially adjusted from the second adjustment circuit,
When the calculated value is equal to or greater than the threshold, the selection unit
Selecting the first adjustment circuit, the second adjustment circuit, and the coupling reduction circuit as adjustment targets;
3. The communication according to claim 2 , wherein a priority order of adjustment is determined for the first adjustment circuit, the second adjustment circuit, and the coupling reduction circuit using the evaluation value and the evaluation function. apparatus. In a communication device including a first antenna and a second antenna,
Calculating a first interference power received from the first antenna;
Calculating a second interference power received from the second antenna;
Calculating a correlation value between the received signal of the first antenna and the received signal of the second antenna;
More than the influence of the gain of the first antenna on the reception performance calculated using the first interference power, the second interference power, and the correlation value, and the reception performance via the first and second antennas A first adjustment circuit that adjusts the gain of the first antenna using an evaluation value that takes a positive value when the influence of the gain of the second antenna on the reception performance is large; and From the second adjustment circuit that adjusts the gain of the antenna, an adjustment circuit that has a greater influence on the reception performance is selected,
An adjustment method, wherein the communication device executes a process of improving the reception performance by giving priority to adjustment of a selected circuit.