JP5674411B2 - Wireless communication apparatus and impedance control method - Google Patents

Description

  The present invention relates to a technique for adaptively controlling the impedance of an antenna, and more particularly to an impedance control technique in a wireless communication apparatus that performs wireless communication by a MIMO (Multiple Input Multiple Output) method.

  Conventionally, in a small wireless communication terminal represented by a mobile phone, it is known that an impedance mismatch occurs due to a change in surrounding environment or a user usage state, resulting in an impedance mismatch and a deterioration in transmission / reception characteristics. Yes. For this reason, many control methods and circuit configurations have been devised that compensate performance by adaptively changing the load impedance of the terminal. For example, in Patent Document 1, the load impedance is adaptively controlled so as to minimize the reflection loss (VSWR) of the antenna and the matching state is ensured.

  On the other hand, when the load impedance is changed, the antenna radiation pattern is changed accordingly, and the antenna propagation characteristics are also changed. In the case of MIMO transmission, the communication performance depends not only on VSWR but also on antenna propagation characteristics such as coupling between antenna elements and propagation channel correlation. Therefore, in Patent Document 2, the MIMO transmission capacity or an evaluation amount according to the MIMO transmission capacity is calculated while changing the antenna load impedance, and adaptive control is performed so that the evaluation amount is maximized.

JP 2005-244340 A JP 2010-053772 A

  However, in Patent Document 2, there are a finite number of load impedance candidates at each antenna end, these are switched, and the load impedances of all the antennas are maximized so that the evaluation amount is the largest among all the load impedance combination candidates of all the antennas. Determine the value. In this configuration, since the number of combinations of impedance candidates of all antennas for calculating the evaluation amount increases exponentially according to the number of antennas and the number of load impedance candidates of each antenna, the search time for determining impedance becomes long, Communication characteristics during that time deteriorate. Further, the followability to temporal changes in the surrounding environment / user usage state and propagation environment is poor, and optimal control cannot be performed. Furthermore, power consumption increases as the number of load impedance switching increases.

  The present invention has been made in view of such circumstances, and reduces the search time for the optimum impedance value by calculating the evaluation amount while efficiently reducing the combination candidates of the impedance candidates of all antennas. An object of the present invention is to provide a wireless communication device and an impedance control technique that can be used.

  (1) In order to achieve the above object, the present invention takes the following measures. That is, the wireless communication apparatus of the present invention is a wireless communication apparatus that includes a plurality of antennas and performs wireless communication using a MIMO (Multiple Input Multiple Output) method, and uses the propagation path estimation information to determine the evaluation amount of the wireless propagation path. An evaluation amount calculation unit to calculate, a reduction candidate number determination unit that reduces the number of impedance combination candidates between the antennas based on the evaluation amount, and an impedance between the antennas corresponding to the reduced number of candidates And an impedance control unit that selects any one of the impedance combinations based on the evaluation amount, and an impedance adjustment unit that adjusts the impedance of each antenna based on the selected impedance combination And.

  Thus, since the number of candidate combinations of impedance between antennas is reduced, the search time for the optimum impedance value can be reduced. As a result, it is possible to quickly follow changes in the input impedance of the communication terminal due to the surrounding environment and user use, and at the same time to control the impedance with a small amount of processing, improving transmission performance and reducing power consumption of the terminal It becomes possible. In addition, the effect of the present invention becomes more significant as the number of antenna elements increases, and therefore, the present invention is very useful in a future wireless communication terminal in which the number of elements is increasing.

  (2) Moreover, in the wireless communication device of the present invention, the reduction candidate number determination unit is configured to combine impedances of the antenna groups for each of a plurality of antenna groups including at least one antenna based on the evaluation amount. The number of candidates is reduced, and the impedance control unit calculates a combination of impedances between the antenna groups corresponding to the reduced number of candidates, and determines any one combination of impedances based on the evaluation amount. The impedance adjustment unit adjusts the impedance of each antenna group based on the combination of the selected impedances.

  Since the antenna group is handled as a group in this way, the impedances of a plurality of antennas included in the same antenna group can be controlled simultaneously. As a result, the search time for determining the impedance can be shortened.

  (3) Moreover, in the wireless communication apparatus of the present invention, the reduction candidate number determination unit increases the number of candidates while the correlation between the antennas or the correlation between the antenna groups is high. When the correlation or the correlation between the antenna groups is low, the number of candidates is reduced.

  In this way, since the number of candidates is changed according to the correlation value, when the correlation value is low, the number of candidates can be greatly reduced, while when the correlation value is high, the decrease in the number of candidates is reduced and the optimum It is possible to reduce the probability of reducing the number of possible impedance combination candidates.

  (4) In the wireless communication device of the present invention, the impedance control unit selects a first antenna or a first antenna group, and impedance of an antenna other than the first antenna or the first antenna group The impedances of antenna groups other than the above are fixed, all the impedance candidates of the first antenna or the first antenna group are calculated, and from the calculated impedance candidates, the transmission capacity or SNR (Signal to Noise Ratio) increases in descending order. A number of impedance candidates corresponding to the number of candidates are selected, and impedance candidates of the second antenna or the second antenna group when the selected impedances are fixed are calculated.

  Thus, the first antenna or the first antenna group is selected, the impedance of the antenna other than the first antenna or the impedance of the antenna group other than the first antenna group is fixed, and the first antenna Since all the impedance candidates of the antenna or the first antenna group are calculated, the number of impedance candidates corresponding to the number of candidates is selected from the calculated impedance candidates in descending order of transmission capacity or SNR (Signal to Noise Ratio). The number of candidates can be reduced by a simple method. As a result, it is possible to quickly follow changes in the input impedance of the communication terminal due to the surrounding environment and user use, and at the same time to control the impedance with a small amount of processing, improving transmission performance and reducing power consumption of the terminal It becomes possible.

  (5) In the wireless communication device of the present invention, the impedance control unit simultaneously changes impedances of the antennas belonging to the same antenna group.

  Thus, since the impedances of the antennas belonging to the same antenna group are changed at the same time, the processing can be simplified. As a result, the search time for determining the impedance can be shortened.

  (6) In the wireless communication device of the present invention, the antenna group is composed of a plurality of antennas having a low inter-element coupling value or antenna correlation value in a frequency band to be communicated. And

  With this configuration, it is possible to configure an antenna group with a plurality of antennas that do not easily affect each other.

  (7) An impedance control method according to the present invention is an impedance control method for a wireless communication apparatus that includes a plurality of antennas and performs wireless communication using a MIMO (Multiple Input Multiple Output) method, and acquires propagation path estimation information. Calculating a wireless channel evaluation amount using the acquired propagation channel estimation information; reducing the number of impedance combination candidates between the antennas based on the evaluation amount; and the reduced candidates Calculating a combination of impedances of the antennas corresponding to the number, selecting one of the impedance combinations based on the evaluation amount, and each of the impedances based on the selected combination of impedances Adjusting the impedance of the antenna, at least comprising: That.

  Thus, since the number of candidate combinations of impedance between antennas is reduced, the search time for the optimum impedance value can be reduced. As a result, it is possible to quickly follow changes in the input impedance of the communication terminal due to the surrounding environment and user use, and at the same time to control the impedance with a small amount of processing, improving transmission performance and reducing power consumption of the terminal It becomes possible. In addition, the effect of the present invention becomes more significant as the number of antenna elements increases, and therefore, the present invention is very useful in a future wireless communication terminal in which the number of elements is increasing.

  (8) In the impedance control method of the present invention, a plurality of antenna groups are configured from a plurality of antennas having low inter-element coupling values or antenna correlation values, and each of the antenna groups is based on the evaluation amount. The number of impedance combination candidates between the antenna groups is reduced, the number of impedance combinations between the antenna groups corresponding to the reduced number of candidates is calculated, and one of the impedances is calculated based on the evaluation amount. A combination is selected, and the impedance of each antenna group is adjusted based on the selected combination of impedances.

  Since the antenna group is handled as a group in this way, the impedances of a plurality of antennas included in the same antenna group can be controlled simultaneously. As a result, the search time for determining the impedance can be shortened.

  According to the present invention, in a communication system using MIMO transmission, the impedance can be controlled with a small amount of processing by following the change in the input impedance of the communication terminal due to the surrounding environment or the user's use, and the transmission performance can be improved. The power consumption of the terminal can be reduced. In addition, the effect of this control method becomes more prominent as the number of antenna elements increases, and it is very useful for future wireless communication terminals in which the number of elements tends to increase.

It is a block diagram which shows schematic structure of the receiver which concerns on this embodiment. It is a flowchart which shows the operation example in the case of a 2 element antenna. It is a figure which shows schematic structure of a 4 element antenna. It is a flowchart which shows the operation example in the case of a 4 element antenna.

  Embodiments of the present invention will be described below with reference to the drawings. In the embodiment of the present invention, the evaluation amount is calculated while efficiently reducing the combination candidates of the impedance candidates of all the antennas. As a result, it is possible to reduce the search time for the optimum impedance value.

  FIG. 1 is a block diagram illustrating a schematic configuration of a receiver according to the present embodiment. This receiver includes K antennas 1a, 1b,..., 1K, and the impedance adjustment unit 2 adjusts the impedance of each antenna 1a, 1b,. Radio signals received by the antennas 1b,..., 1K are processed by the receiving circuits 3a, 3b,..., 3K, respectively, and restored by the demodulation / decoding unit 4 as data. The channel estimation unit 5 estimates the propagation path state of the radio signal, and outputs the estimation result to the demodulation / decoding unit 4 and the evaluation amount calculation unit 6.

  The evaluation amount calculator 6 calculates a transmission capacity, an SNR (Signal to Noise Ratio), and an inter-antenna correlation value based on the propagation path estimation information. The reduction candidate number determination unit 7 deletes the number of impedance combination candidates for each antenna by a method described later. The impedance control unit 8 selects one of the impedance combinations of the antennas 1a, 1b,..., 1K based on the determined number of candidates and the evaluation amount.

The impedance of each antenna 1a, 1b,..., 1K is adaptively adjusted by the impedance adjustment unit based on a control signal from the impedance control unit. Let M be the number of impedance candidates used for each antenna and m _k be the index. Incidentally, at this time, the combination number of candidates of the impedance of the entire antenna is M ^K pieces. However, each antenna may have a different number of impedance candidates. Further, it is assumed that the impedance candidate index can be reassigned every time a search is performed.

Evaluation value calculation section 6, the current impedance value obtained by the channel estimation unit 5 m _1, m _{2, ...} transmission capacity of the reception, which is calculated using the received channel response in _{m K C (m 1, m} 2, ... m _K ), the reception SNR of each antenna and the correlation value between the antennas are calculated and notified to the impedance control unit 8.

Next, the processing flow of the impedance control unit 8 will be described. Let the antenna index be k. The impedance control unit 8 fixes the impedance values of the (k + 1) th and higher antennas in order from k = 1 to a constant value, and based on the transmission capacity calculated in the process of changing the impedances of the kth antenna for all candidates, k antenna to the impedance combination candidate number of reducing the _{N k-number (N} k << ^{M k).} This operation is performed until k = K, and the combination of antenna impedances having the highest transmission capacity is determined from the remaining combination candidates.

The number of surviving combination candidates N _k to be left in each step is adaptively determined by the reduction candidate number determination unit 7 based on the correlation value between antennas calculated by the evaluation amount calculation unit 6. This reduction candidate number determination unit 7 increases N _k when the correlation value between the k-th antenna whose impedance is changed and other antennas is high, and controls N _k when the correlation is low. However, the configuration may be such that N _k is determined by a combination of the average SNR of all antennas and the correlation value. In the case of having three or more antenna elements, there are two or more antenna combinations. In this case, the number of reduction candidates is determined using a result of statistical processing performed on a plurality of correlation values obtained. For example, the maximum correlation value or the median value is used.

Next, a candidate reduction process flow is shown. First, the number of antenna k = 1 candidates is reduced to N ₁ . The antenna impedances m ₂ ,... m _K of k = 2, 3,... K are fixed, and the transmission capacity C (m ₁ , m _{2 is set} for all the impedance candidates (m ₁ = 1, 2,. ,... M _K ). From the calculation result, N ₁ candidate impedances of the antenna 1a having a large transmission capacity are left.

Then, to reduce left behind the antenna 1a _{N 1} pieces of candidates and the antenna 1b M pieces impedance candidate combinations _{N 1} M pieces of the to _{two N.} In this step, the antenna impedance of k = 3,... K is fixed, the transmission capacity is calculated for N ₁ M combination candidates, and N ₂ impedance combinations with large transmission capacity remain. This reduction process is repeated until k = K, and the candidate having the highest transmission capacity is selected from the remaining combinations of impedance combinations. Thereby, the search time can be shortened and the impedance of each antenna can be selected efficiently.

  Note that all the antennas of the terminal may be grouped into a plurality of antenna groups to which at least one antenna belongs, and the candidate reduction process may be performed in units of antenna groups. At this time, the impedances of two or more antennas belonging to the same group can be changed at the same time, and an impedance value having a high SNR is left as a candidate for each antenna. Note that combinations of antennas having low inter-element coupling effects and low correlation between antennas are predicted in advance from the arrangement and configuration of antennas, and these are grouped into the same group. Thus, the search time can be further reduced by simultaneously changing the impedances of a plurality of antennas that are unlikely to influence each other and independently determining the surviving impedance candidates.

Next, an embodiment in the case of a two-element antenna will be described. When the wireless communication apparatus has two antennas, the configuration is the same as that in FIG. FIG. 2 is a flowchart showing an operation example in the case of a two-element antenna. First, the impedance (index) of the antenna 1b is fixed to m ₂ = 0, the impedance of the antenna 1a is changed by M candidates, and the transmission capacity and antenna correlation value at each candidate value at that time are calculated. Next, an R (m ₁ m ₂ ) average value of correlation values between antennas for M candidates is calculated, and N ₁ is determined by the reduction candidate number determination unit 7. The reduction candidate number determination unit 7 determines N ₁ based on the correspondence table shown in the following table. However, a correspondence table may be prepared for each average SNR of all antennas, and the numerical correspondence is not limited to this table.

Next, the impedance candidate index transmission capacity is large from the impedance of the antenna 1a which is the M change detecting _one N. Let these indices be m ₁ (i). However, i = 1, 2,... N ₁ . Then, the impedance of the antenna 1a, when secured to each of i = 1 through i = N _1, the impedance index m ₂ antenna 1b, is varied from 1 to M-1, the transmission capacity is increased most A combination of (m ₁ , m ₂ ) is obtained, and the impedance value of each antenna is fixed to each value.

That is, in FIG. 2, m ₁ = 0 and m ₂ = 0 are set (step S1), and the transmission capacity C (m ₁ , m ₂ ) is calculated (step S2). Next, it is determined whether or not m ₁ ≦ M−1 (step S3). If m ₁ ≦ M−1 is not satisfied, 1 is added such that m ₁ = m ₁ +1 (step S4). Transition to step S2. On the other hand, if m ₁ ≦ M−1 in step S3, the number of m ₁ candidates is reduced to N ₁ (step S5). That is, in step S5, N ₁ candidate impedance indexes having a large transmission capacity are extracted. Next, i = 1 (step S6), m ₁ =, m ₁ (1), m ₂ = 1, and the transmission capacity C (m ₁ , m ₂ ) is calculated (step S8).

Next, it is determined whether or not m ₂ ≦ M−1 (step S9). When m ₂ ≦ M−1 is not satisfied, 1 is added such that m ₂ = m ₂ +1 (step S10). The process proceeds to step S8. On the other hand, if m ₂ ≦ M−1 in step S9, it is determined whether i ≦ N ₁ (step S11). If i ≦ N ₁ , i = i + 1 is set (step S12). The process proceeds to step S7. On the other hand, in step S11, if it is i ≦ _{N 1,} the transmission capacity _{C (m} 1, m ₂₎ is selected _m 1, _{m 2,} which becomes the maximum.

  In the above description, the transmission capacity is used as an index. However, the present invention is not limited to this, and evaluation quantities such as throughput and packet error rate may be used.

Next, an embodiment in the case of a four-element antenna will be described. FIG. 3 is a diagram showing a schematic configuration of a four-element antenna. As shown in FIG. 3, it is assumed that the distance between the antennas of the element 1 and the element 2 is far from the arrangement of the antenna elements on the substrate, and the impedance control results do not greatly influence each other. Therefore, antennas are grouped into the following three antenna groups.
Antenna group 1: antenna 1 and antenna 2
Antenna group 2: Antenna 3
Antenna group 3: Antenna 4

FIG. 4 is a flowchart showing an operation example in the case of a four-element antenna. First, the impedances of the antenna 3 and the antenna 4 are fixed to m ₃ = 0 and m ₄ = 0, the impedances of the antenna 1 and the antenna 2 are simultaneously changed from index 1 to M, and the SNR at each index is calculated. 1, the antenna 2 detects _{one N} impedance candidates SNR increases respectively, to reduce the number of combinations of impedances candidate antenna 1, antenna 2 (antenna group 1) _N ^{1 2.} Next, the impedance index of the antenna element 4 is fixed to m _{4 =} 0, for each candidate combination of the impedance of the N ₁ ² single antenna 1 antenna 2, the impedance candidate m ₃ of the antenna 3 from 1 to M The transmission capacity when changed is calculated, and the number of candidate combinations of antenna 1, antenna 2 and antenna 3 is reduced to N ₂ having a large transmission capacity. Finally, the transmission capacity when m ₄ is changed is calculated for each of the N ₂ antenna 1, antenna 2, and antenna 3 impedance combination candidates, and the combination of impedance candidates with the largest transmission capacity is detected. And fix to the same value.

That is, in FIG. 4, first, the impedance candidates of the antennas 1 to 4 are set to m ₁ = 0, m ₂ = 0, m ₃ = 0, m ₄ = 0 (step S21), and then SNR (m ₁ ) and SNR (m ₂ ) are calculated (step S22). Next, it is determined whether or not m ₁ ≦ M−1 (step S23). If m ₁ ≦ M−1 is not satisfied, m ₁ = m ₁ +1 and m ₂ = m ₂ +1 are set (step S24). The process proceeds to step S22.

On the other hand, if m ₁ ≦ M−1 in step S23, the number of candidates for m ₁ and m ₂ is reduced to N ₁ each (step S25). At this time, the number of combinations of the number of candidates for the antenna 1 and the antenna 2 is N ₁ ² , and g (1), g (2),... G (N ₁ ² ), respectively. Next, i = 1 (step S26), and m ₃ = 1 (step S27). Then, the transmission capacity C (g (i), m ₃ , m ₄ ) is calculated (step S28), and it is determined whether or not m ₃ ≦ M−1 (step S29). In step S29, when m ₃ ≦ M−1 is not satisfied, m ₃ = m ₃ +1 is set (step S30), and the process proceeds to step S28. On the other hand, in step S29, if it is _{m 3} ≦ _M-1, determines whether i ≦ _N ^{1 2} (step S31), and if not i ≦ _N ^{1 2,} as i = i + 1 (step S32 ), And the process proceeds to step S27.

On the other hand, if i ≦ N ₁ ² in step S31, the number of combination candidates of antenna 1, antenna 2, and antenna 3 is reduced to N ₂ (step S33). Accordingly, g ⁽²⁾ (1), g ⁽²⁾ (2),... G ⁽²⁾ (N ₂ ) are obtained. Then, j = 1 as (step _S34), and the _m 3 = 1 (step S35). Then, the transmission capacity C (g ⁽²⁾ (j), m ₄ ) is calculated (step S36), and it is determined whether m ₄ ≦ M−1 (step S37). In step S37, if m ₄ ≦ M−1 is not satisfied, m ₄ = m ₄ +1 is set (step S38), and the process proceeds to step S36. On the other hand, if m ₄ ≦ M−1 in step S37, it is determined whether j ≦ N ₂ (step S39). If i ≦ N ₂ is not satisfied, j = j + 1 is set (step S40). Transition to step S35. On the other hand, in step S39, if it is i ≦ _{N 2} is selected the transmission capacity _{C (m 1, m 2,} m 3, m 4) is maximum _{m 1, m 2, m 3} , m 4.

  As described above, according to the present embodiment, in a communication system using MIMO transmission, it is possible to control the impedance with a small amount of processing, following a change in the input impedance of the communication terminal due to the surrounding environment or the user at high speed. It is possible to improve the transmission performance and reduce the power consumption of the terminal. In addition, the effect of this control method becomes more prominent as the number of antenna elements increases, and it is very useful for future wireless communication terminals in which the number of elements tends to increase.

1a to 1K Antenna 2 Impedance adjustment units 3a to 3K Reception circuit 4 Demodulation / decoding unit 5 Channel estimation unit 6 Evaluation amount calculation unit 7 Reduction candidate number determination unit 8 Impedance control unit

Claims (8)

A wireless communication device that includes a plurality of antennas and performs wireless communication using a MIMO (Multiple Input Multiple Output) method,
An evaluation amount calculation process for selecting any antenna from the plurality of antennas, fixing impedances of antennas other than the selected antenna, and calculating evaluation amounts corresponding to all candidates of the impedance of the selected antenna, An evaluation amount calculation unit that repeats until there are no unselected antennas,
For each of the evaluation value calculation processing, and on the basis of the evaluation amount, reducing the number-of-candidates determining unit to reduce candidates of the impedance of the selected antenna,
Based on the evaluation amount obtained by the evaluation amount calculation process repeated until the unselected antenna disappears, an impedance control unit that selects any one of the impedance combinations;
An wireless communication apparatus comprising: an impedance adjustment unit that adjusts the impedance of each antenna based on the selected combination of impedances. The evaluation amount calculation unit selects an antenna group including at least one antenna, fixes an impedance of an antenna other than the antenna included in the selected antenna group, and sets an impedance of each antenna included in the selected antenna group. As the same, the evaluation amount calculation process for calculating the evaluation amount corresponding to all the impedance candidates of each antenna is repeated until there is no unselected antenna group,
The reduction candidate number determining unit reduces the impedance candidates of each antenna included in the selected antenna group based on the evaluation amount for each evaluation amount calculation process,
The impedance control unit selects any one combination of impedances based on the evaluation amount obtained by the evaluation amount calculation process repeated until the unselected antenna group disappears,
The wireless communication apparatus according to claim 1, wherein the impedance adjustment unit adjusts the impedance of each antenna based on the selected combination of impedances.   2. The reduction candidate number determination unit increases the number of candidates when the correlation between the antennas is high, and decreases the number of candidates when the correlation between the antennas is low. Or the radio | wireless communication apparatus of Claim 2. 3. The wireless communication apparatus according to claim 1, wherein the impedance control unit selects a combination of impedances that maximizes transmission capacity or SNR (Signal to Noise Ratio).   3. The radio communication apparatus according to claim 2, wherein the antenna group includes a plurality of antennas having low inter-element coupling values or antenna correlation values within a frequency band that is a target when performing communication. An impedance control method for a wireless communication apparatus that includes a plurality of antennas and performs wireless communication using a MIMO (Multiple Input Multiple Output) method,
The first antenna is selected from the plurality of antennas, the impedances of the antennas other than the first antenna are fixed, the evaluation quantities corresponding to all the impedance candidates of the first antenna are calculated, and the evaluation quantities Based on the above, the number of impedance candidates of the first antenna is reduced, a new antenna is selected from antennas other than the already selected antenna, the impedance of the unselected antenna is fixed, and the impedance of the newly selected antenna is selected. All antennas select to calculate the evaluation amount corresponding to the combination of all candidates and the remaining candidate of the already selected antenna, and to reduce the antenna impedance combination candidates based on the calculated evaluation amount Repeat until
Based on the finally calculated evaluation amount, select any one of the impedance combinations,
An impedance control method for adjusting the impedance of each antenna based on the selected combination of impedances. Configure multiple antenna groups from multiple antennas with low inter-element coupling values or low antenna correlation values,
Based on the evaluation amount, for each of the antenna groups, to reduce the impedance combination candidate between the antenna groups,
Calculate a combination of impedances between the number of antenna groups corresponding to the reduced candidates, and select any one impedance combination based on the evaluation amount,
The impedance control method according to claim 6, wherein the impedance of each antenna group is adjusted based on the selected combination of impedances. 8. The impedance control method according to claim 6 or 7, wherein a combination of impedances having a maximum transmission capacity or SNR (Signal to Noise Ratio) is selected.

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