JP4435098B2 - Wireless communication apparatus and wireless communication method - Google Patents

Description

  The present invention uses the same frequency channel, spatially multiplexes and transmits independent signal sequences from a plurality of different transmission antennas, receives signals using a plurality of reception antennas, and determines a transfer function matrix between the transmission and reception antennas. The present invention relates to a high-speed wireless access system that realizes MIMO (Multiple-Input Multiple-Output) communication that demodulates data on the receiving station side, and one wireless communication device and a plurality of other wireless communication devices simultaneously and at the same frequency The present invention relates to a wireless communication apparatus and a wireless communication method that perform spatial multiplexing on a channel.

  In recent years, the IEEE802.11g standard, the IEEE802.11a standard, and the like are remarkable as high-speed wireless access systems using the 2.4 GHz band or the 5 GHz band. In these systems, an orthogonal frequency division multiplexing (OFDM) modulation method, which is a technique for stabilizing characteristics in a multipath fading environment, is used, and a transmission rate of 54 Mbps at the maximum is realized.

  However, the transmission rate here is a transmission rate on the physical layer. Actually, the transmission efficiency in the MAC (Medium Access Control) layer is about 50 to 70%. The value is about 30 Mbps. On the other hand, in the world of wired LAN, the provision of a 100 Mbps high-speed line using FTTH (Fiber to the home) using an optical fiber has been widespread in each home, including the Ethernet (registered trademark) 100Base-T interface. In the world of wireless LAN, further increase in transmission speed is demanded.

  As a technology for that purpose, the MIMO technology is promising. This MIMO technology is such that different independent signals are transmitted on the same channel from a plurality of transmitting antennas on the transmitting station side, and signals are received on the receiving station side using the same plurality of antennas. The transfer function matrix is obtained, the independent signal transmitted from each antenna is estimated on the transmitting station side using this matrix, and the data is reproduced.

  It is known that the theoretical maximum transmission capacity C using the MIMO technology can be theoretically obtained by the following formula (1) (for example, see Non-Patent Document 1).

In the above equation (1), ρ is a signal-to-noise power ratio, M is the number of transmitting antenna elements, and _IN is a unit matrix of the number of receiving elements N × N. H is a transfer function matrix representing the propagation channel response between the transmitting antenna and the receiving antenna, and can be described by the following equation (2).

Here, h _ij is the channel response of the propagation path from the i-th transmitting antenna to the j-th receiving antenna. From Equation (1), in MIMO transmission, an increase in the number of antenna elements, an increase in SNR, and a decrease in spatial correlation between antennas lead to an increase in transmission capacity. Of these, increasing the number of antenna elements most effectively leads to an increase in transmission capacity for MIMO transmission. However, since the increase in the number of antenna elements directly leads to an increase in the hardware scale of the wireless communication apparatus, it is necessary to perform MIMO transmission with as few elements as possible and obtain the maximum effect. In particular, the terminal station needs to mount a transmitter, a receiver, an antenna, and the like in a limited space, and the number of antenna elements needs to be at most about several elements.
I. E. Telatar, “Capacity of multi-tenenna Gaussian channels”, Euro. Trans. Telecommun. , Vol. 1, no. 6, Nov. / Dec. 1999.

  The MIMO transmission capacity described above represents the capacity when transmission is performed using a theoretically optimal modulation scheme, encoding, or the like with a given SNR. In practice, the transmission capacity of Equation (1) is used. Can't get capacity. In fact, it has been reported that the characteristics vary greatly depending on the decoding process on the receiving side. This fact is disclosed, for example, in “Literature: Daibell, MIMO system basics and elemental technology, antenna / propagation design / analysis method workshop, W29, 30”.

  Here, the characteristics of the ZF (Zero Forcing) method and the MMSE (Minimum Mean Square) method, which are known as simple decoding, may greatly deteriorate due to the correlation between antennas. On the other hand, by using a method such as OSUC (Ordered Successive Cancellation) or MLD (Maximum Likelihood Detection), good transmission characteristics can be obtained even when the correlation between antennas becomes relatively large. However, there is a tradeoff between performance and computational complexity for these methods. That is, if the performance is to be improved, there arises a problem that the burden on the signal processing unit increases.

  In addition, as a technique for realizing good MIMO transmission performed by a simple decoding process such as a ZF (Zero Forcing) method or a MMSE (Minimum Mean Square) method, a weighted SDM (Space Division Multiplexing) method (W-SDM method) is used. Proposed.

  FIG. 7 is a block diagram showing a configuration of a wireless communication apparatus using the W-SDM method according to the prior art. In the figure, in the W-SDM method, first, the number of antennas more redundant than the number of data to be transmitted is arranged on the transmission side. The propagation channel estimation unit 7 estimates all transfer functions between the receiving antenna and the redundant number of transmitting antennas. Using the estimated propagation channel information of all combinations of transmission / reception antennas, the transmission capacity expectation value calculation unit 8 transmits the number of transmission data, the number of transmission antennas, and the antenna number to be transmitted when the number of transmission antennas and the number of transmission data are determined. The transmission capacity C given by Equation (1) is calculated for all combinations from # 1 to #L in FIG. In accordance with the result obtained by this calculation, the transmission antenna selection unit 9 determines the transmission antenna based on the number of transmission antenna elements and the antenna number that have the largest expected capacity value. The transmission antenna control unit 10 switches the switch 4 to connect the selected transmission antenna to the transmitter so as to use the determined transmission antenna.

  If this method is used, a combination of antennas having high SNR (Signal-to-Noise Ratio) and low correlation between antennas is selected by having redundant antennas. Can be decrypted. However, in this method, when the number of redundant antenna elements is increased, the transmission capacity expected value calculation unit 8 needs to calculate a combination for an enormous transmission capacity, so that simple processing can be realized on the receiving side. Even if it can, the problem that the computation on the transmission side becomes enormous arises.

  The present invention has been made in view of such circumstances, and an object of the present invention is to switch the antenna element according to a simpler standard than the W-SDM method and transmit the signal so that the decoding process on the receiving side is the ZF method. An object of the present invention is to provide a wireless communication apparatus and a wireless communication method capable of improving MIMO transmission characteristics even if the processing is relatively simple, such as the MMSE method.

In order to solve the above-described problem, the present invention includes a first antenna group including four or more antennas, and includes a plurality of antennas included in the first antenna group and another wireless communication device. A wireless communication apparatus that performs MIMO communication by spatially multiplexing a plurality of signal systems at the same frequency channel and at the same time through a MIMO channel configured by the second antenna group, the wireless communication apparatus and the other Received power estimation means for estimating received power of each antenna of the first antenna group using a channel response value of a propagation path between the first antenna group and the first antenna group, A first antenna selecting means for selecting a plurality of antennas having relatively large received power estimated by the received power estimating means; and a plurality of antennas selected by the first antenna selecting means. Correlation value calculating means for calculating a correlation value between a plurality of antennas and antennas other than the plurality of antennas, and an antenna having a relatively small correlation value calculated by the correlation value calculating means. Second antenna selection means for selecting at least one of the other antennas, and transmission means for transmitting a signal using the antenna selected by the first antenna selection means and the second antenna selection means, It is characterized by comprising.

According to the present invention, in the above invention, the first antenna group is composed of L (L is an integer of 4 or more) antenna elements, the second antenna group is composed of N antenna elements, The received power estimation means includes a propagation channel estimation means for estimating a propagation channel response transmitted from the other radio communication device, and the L antennas based on the propagation channel response value estimated by the propagation channel estimation means. Receiving power calculation means for calculating the received power obtained by each of the elements, wherein the first antenna selection means receives the received power calculated by the received power calculation means from the first antenna group. K (K <L) relatively large antenna elements are selected, and the correlation value calculating means includes the selected K antenna elements and (L−K) antenna elements. (L−K) spatial correlations are calculated, and the second antenna selection unit selects an antenna element having a relatively small spatial correlation value from P− (L−K) antenna elements. P <L−K) This selection is characterized.

In order to solve the above-described problem, the present invention provides a first wireless communication apparatus including a first antenna group including four or more antennas and a second antenna group including a plurality of antennas. A plurality of signal systems in the same frequency channel and at the same time through a MIMO channel configured by the first antenna group and the second antenna group. A wireless communication method for performing MIMO communication in a multiplexed manner, wherein received power for each first antenna is obtained using a channel response value of a propagation path between the first wireless communication device and the second wireless communication device. A second step of selecting a plurality of antennas having a relatively large estimated received power from the first antenna group, and the selected plurality of antennas. A third step of calculating a correlation value between the antenna other than the plurality of antennas and an antenna having a relatively small calculated correlation value from among the antennas other than the plurality of antennas. A fourth step of selecting one, and a fifth step of transmitting a signal using a plurality of antennas having a relatively large received power and at least one antenna having a relatively small correlation value. It is characterized by that.

According to the present invention, in the above invention, the first antenna group is composed of L (L is an integer of 4 or more) antenna elements, the second antenna group is composed of N antenna elements, In the first step, a propagation channel response transmitted from the second wireless communication apparatus is estimated, and received power obtained by each of the L antenna elements based on the estimated propagation channel response value In the second step, K (K <L) antenna elements with relatively large received power calculated by the received power calculating means are selected from the first antenna group, In the third step, (L−K) spatial correlations are calculated for each of the selected K antenna elements and (L−K) antenna elements, and in the fourth step, ( Among -K) the antenna elements, and selects the spatial correlation value is relatively small antenna elements P (P <L-K).

  The present invention is the above invention, wherein the antenna element of the first wireless communication device is an antenna element having at least two different polarization characteristics, and the received power of the antenna element is measured for each polarization characteristic. A sixth step of determining the combination of the antenna elements based on the polarization characteristics of the antenna elements, the received power of the antenna elements measured for each polarization characteristic, and the And an eighth step of determining an antenna element to be used for transmission based on the determined combination of antenna elements.

  The present invention is characterized in that, in the above invention, when there are a plurality of the second wireless communication devices, the first to fifth steps are performed for each of the second wireless communication devices. And

  According to the present invention, each of the first antenna groups is obtained by using the channel response value of the propagation path between the first antenna group constituted by a plurality of antennas and the other wireless communication device by the reception power estimating means. The first antenna selection unit selects a plurality of antennas having a relatively large estimated reception power from the first antenna group, and the correlation value calculation unit selects the received power. The correlation value between the plurality of antennas selected and the antenna other than the plurality of antennas is calculated, and an antenna having a relatively small correlation value is selected by the second antenna selection unit as an antenna other than the plurality of antennas. Then, at least one is selected and a signal is transmitted by the transmission means using the selected antenna. Therefore, by switching and transmitting antenna elements according to a simpler standard than the W-SDM method, even if the decoding process on the receiving side is a relatively simple process such as the ZF method or the MMSE method, MIMO transmission is performed. The advantage that the characteristics can be improved is obtained.

  Hereinafter, a wireless communication apparatus according to an embodiment of the present invention will be described with reference to the drawings.

A. First Embodiment FIG. 1 is a block diagram showing a configuration of a wireless communication apparatus according to a first embodiment of the present invention. Note that portions corresponding to those in FIG. FIG. 1 shows a mode in which the first wireless communication apparatus 300 operates as a transmission side and the second wireless communication apparatus 200 finally operates as a reception side. The first and second wireless communication apparatuses 300 and 200 operate as a base station and a terminal, respectively. In addition, including the subsequent embodiments, the number of signal systems that the first radio apparatus performs spatial multiplexing is assumed to be M ′. Note that the value of M ′ may be adaptively changeable.

The first wireless communication apparatus 300 includes a transmission signal generation unit 1, M (M ≧ M ′) transmitters 2-1 to 2-M, circulators 3-1 to 3-M, a switch 4, and L antennas. # 1 to #L, M receivers 6-1 to 6-M, a propagation channel estimation unit 7, an SNR estimation unit 30, a correlation value calculation unit 31, a transmission antenna selection unit 9, and a transmission antenna control unit 10 Yes. Transmission signal generating unit 1 generates a M 'number of transmitted signals _S 1 to S _M', and supplies to the transmitter 2-1 to 2-M '. The transmitters 2-1 to 2-M ′ transmit signals from the selected M ′ transmitting antennas via the circulators 3-1 to 3-M and the switch 14. The selection of the transmission antenna will be described later.

  In first wireless communication apparatus 300, since L> M, signals cannot be received by L antennas at a time. Therefore, the propagation channel response is estimated for every M antennas. The SNR estimation unit 30 ranks L SNRs and selects K antennas (K <M ′) having relatively large SNRs. The correlation value calculation unit 31 combines K antennas and P of the remaining (LK) lines so that the SNR is high, calculates the correlation value in each combination, and the correlation value is low. As such, P antenna elements are selected as transmitting antennas.

  The transmission antenna selection unit 9 instructs the transmission antenna control unit 10 on information on the selected antenna. The transmission antenna control unit 10 switches and controls the switch 4 so as to connect the selected antenna and the transmitters 2-1 to 2-M in accordance with the above command. The switch 4 connects the antennas # 1 to #L and the transmitters 2-1 to 2-M or the receivers 6-1 to 6-M according to switching control by the transmission antenna control unit 10.

  The second wireless communication apparatus 200 includes a propagation channel estimation signal transmitter 11, transmitters 12-1 to 12-N, circulators (or switches) 13-1 to 13-N, and N antennas # 1 to #N. , N receivers 14-1 to 14 -N, a propagation channel estimation unit 15, and a decoding processing unit 16. The propagation channel estimation signal transmitter 11 generates a propagation channel estimation signal Sp. Transmitters 12-1 to 12-N transmit propagation channel estimation signal Sp from antennas # 1 to #N to first radio communication apparatus 300 via circulators 13-1 to 13-N.

  The receivers 14-1 to 14-N receive signals from the first wireless communication apparatus 200 by the antennas # 1 to #N via the circulators 13-1 to 13-N. The propagation channel estimation unit 15 estimates the propagation channel response from the signals received by the receivers 14-1 to 14-N. The decoding processing unit 16 decodes the received signal.

  In the first embodiment, the propagation channel response is estimated from the signal transmitted by the second wireless communication apparatus 200. However, the signal transmitted by the first wireless communication apparatus 300 is estimated by the second wireless communication apparatus 200. The estimation result may be fed back to the first wireless communication apparatus 300.

  Next, FIG. 2 is a flowchart for explaining the operation of the wireless communication apparatus according to the first embodiment. First, in the second wireless communication apparatus 200, the propagation channel estimation signal transmitter 11 transmits a propagation channel estimation signal by the transmitters 12-1 to 12-M (S1). On the other hand, in the first wireless communication apparatus 300, the propagation channel estimation signals are received by the receivers 6-1 to 6-M, and the propagation channel estimation unit 7 estimates the propagation channel response (S2). .

  At this time, in the first wireless communication apparatus 300, since M of the receivers 6-1 to 6-M, the number of antennas is L, and L> M, signals are transmitted with L antennas at a time. Cannot receive. Therefore, first wireless communication apparatus 300 estimates the propagation channel response for each of M antennas. For example, when L = 8 and M = 3, estimation is performed with combinations such as # 1 to # 3, # 4 to # 6, # 7, and # 8.

Next, in the first wireless communication apparatus 300, the SNR estimator 30 obtains received power or SNR according to the estimated propagation channel information (S3). Assuming that the propagation channel response of the N × L MIMO channel corresponding to the propagation channel response of Equation (2) is obtained in step S2, SNR _{i at} the i-th (i = 1 to L) receiving antenna is It can be obtained by Equation (3).

  Next, in the first wireless communication apparatus 300, the SNR estimation unit 30 ranks the L SNRs in descending order, and sends information on the K reception antennas having the largest SNRs to the transmission antenna selection unit 9 (S4). ). Here, K <L. Selecting an antenna element having a high SNR can be expected to increase the capacity of MIMO. However, as described above, it is also important for MIMO transmission that the correlation value between antennas is as low as possible. Therefore, in the first embodiment, K antennas that increase the SNR and P of the remaining (LK) are combined, and the correlation value calculation unit 31 calculates the correlation value in each combination. The calculation is performed (S5), and the transmission antenna selection unit 9 selects P antenna elements having a low correlation value, and sends information on the P antenna elements to the transmission antenna selection unit 9 (S6). Here, the conditions of P <L−K and K + P = M ′ are satisfied.

  As an example, a case where there are four transmission antennas and four reception antennas will be described. The channel matrix is obtained by the above-described equation (2) (M = 4, N = 4). Here, first, it is assumed that two (K = 2) antenna elements having a large SNR and one (P = 1) antenna element having a low correlation with these are selected. The antennas with large SNR are # 2 and # 4, and the remaining one antenna from # 1 and # 3 is selected using the correlation value.

In this case, the correlation value [rho ₃ for the correlation value [rho _1, and the antenna # 3 for antenna # 1, the following equation (4) is given by (5).

The above formulas (4) and (5) are the correlation sum between the antenna to be selected and the already selected antenna. In equations (4) and (5), the first term on the right side corresponds to the correlation with antenna # 2, and the second term corresponds to the correlation with antenna # 4. The correlation values ρ ₁ and ρ ₃ are compared, and the antenna having the smaller value may be selected as the third antenna element. In the case of selecting two or more antenna elements, antenna elements having a small correlation value may be selected in order according to the above mathematical formula. When the number of transmitters and receivers is M, for example, K may be M-1, and one of LK may be selected, or K may be M-2. One may be selected from LK.

Next, the transmission antenna selection unit 9 selects an antenna element to be used according to the information on the K antenna elements having a large SNR and the information on the P antenna elements having a low correlation value, and selects the antenna elements to be used. Information is sent to the transmitting antenna control unit 10 (S7). The transmission antenna control unit 10 switches the switch 4 so that the selected antenna element and the transmitters 2-1 to 2-M ′ are connected according to the information of the selected antenna element (S8). Thereafter, the first wireless communication station 300 transmits the signals S _{1 to} S _{M ′} generated by the transmission signal generation unit 1 from the selected M ′ transmission antennas (S9). On the other hand, in the second radio communication station 200, the propagation channel estimation unit 15 estimates the propagation channel response (S10), and the decoding processing unit 16 decodes the received signal (S11).

B. Second Embodiment Next, a second embodiment of the present invention will be described.
FIG. 3 is a block diagram showing the configuration of the wireless communication apparatus according to the second embodiment. The second embodiment is an example extended to multi-user MIMO. It should be noted that portions corresponding to those in FIG. In the second embodiment, the first wireless communication apparatus 301 performs the second wireless communication so that the transmission antennas for each of the plurality of second wireless communication apparatuses (terminals) 200-1 and 200-2 can be determined. Each of the devices 200-1 and 200-2 has the basic function shown in FIG. Furthermore, the first wireless communication apparatus 301 has a function of detecting a correlation between terminals so that interference between terminals does not increase when the selected antenna is used.

  The first wireless communication device 301 includes signal processing units 40-1 and 40-2 for each second wireless communication device. The signal processing units 40-1 and 40-2 are the propagation channel estimation unit 7, the SNR estimation unit 30, the correlation value calculation unit 31, the transmission antenna selection unit 9, and the transmission antenna control described in the first embodiment, respectively. Part 10 is provided. In addition, the inter-terminal correlation monitoring unit 41 uses the second radio communication device 200-so that interference between the second radio communication devices 200-1 and 200-2 does not increase when the selected antenna is used. The correlation between 1 and 200-2 is detected.

  In the configuration described above, the correlation between the terminals is detected by the correlation monitoring unit 41 between terminals, and when the correlation value between the terminals becomes large, it is avoided as a terminal to be connected at the same time, or the antenna to be transmitted is a candidate in advance. The processing such as selecting again from the top of the selected antenna element is performed.

C. Third Embodiment Next, a third embodiment of the present invention will be described. The third embodiment is an example extended to multi-user MIMO. The point of the third embodiment lies in the fact that even when vertically and horizontally polarized antenna elements are close to each other, the correlation is greatly reduced as compared to the case where the same polarized waves are closely arranged. Therefore, in the third embodiment, by selecting an antenna having a high SNR in advance, the SNR is based only on the information about the antenna position and the polarization without having to bother to obtain the correlation value. The antenna can be selected so that the correlation between the antennas is high and the correlation between the antennas is low.

  FIG. 4 is a block diagram showing the configuration of the wireless communication apparatus according to the third embodiment. It should be noted that portions corresponding to those in FIG. In the figure, the antenna 4-1 is composed of vertically and horizontally polarized antenna elements. The polarization-specific SNR estimation unit 50 measures the SNR for each antenna having different polarization characteristics. The combination pattern table unit 51 stores tabulated values so that different polarization elements that are as close as possible are selected so that the correlation with the selected high SNR antenna element is low.

  As a combination pattern, for example, when selecting the first K lines, a combination of only vertically polarized waves (priority is given to higher SNR) is selected in advance, and when selecting the next P lines, Horizontal polarization is selected as a combination of antennas with low correlation. For example, it is generally known that the vertical polarization antenna is first preferentially selected because the vertical polarization SNR is slightly higher than the horizontal polarization SNR. Since very low correlation is obtained between antennas, it is effective in the sense that a combination with low correlation can be obtained.

  Or it is good also as a combination (it assumes that it selects so that a correlation may become low in the first place) which changes a polarization alternately in order with vertical, horizontal, vertical, horizontal, .... This is because in an environment where the spatial correlation is high, such as outdoors, the correlation is very high with vertical polarization alone. Means.

  As described above, in the third embodiment, first, an antenna element having a high SNR is selected for each polarization, and thereafter, antenna elements having different polarizations may be selected for adjacent elements. Therefore, the transmission antenna selection unit 9 selects in advance antenna elements having different polarizations in order to determine which antenna element has a different polarization among adjacent antenna elements with a high SNR. The combination pattern table unit 51 is referred to. In this way, by making a table, it is possible to efficiently determine a transmission antenna without obtaining a correlation value.

  FIG. 5 is a flowchart for explaining the operation of the wireless communication apparatus according to the third embodiment. First, in the second wireless communication apparatus 200, the propagation channel estimation signal transmission unit 11 transmits a propagation channel estimation signal using the transmitters 12-1 to 12-N (S20). On the other hand, in the first wireless communication apparatus 302, the propagation channel estimation signals are received by the receivers 6-1 to 6-M, and the propagation channel estimation unit 7 estimates the propagation channel response (S21). .

  At this time, in the first wireless communication apparatus 302, since M of the receivers 6-1 to 6-M, the number of antennas is L, and L> M, signals are transmitted with L antennas at a time. Cannot receive. Therefore, the first wireless communication apparatus 302 estimates the propagation channel response for each M antennas. For example, if L = 8 and M = 3, first, estimation is performed for # 1 to # 3, then estimation is performed for # 4 to # 6, and finally the remaining two, # 7 and # 8. Estimate for.

Next, in the first wireless communication apparatus 302, the polarization-specific SNR estimation unit 50 obtains the received power or SNR according to the estimated propagation channel information (S22). Assuming that the propagation channel response of the N × L MIMO channel corresponding to the propagation channel response of Equation (2) is acquired in step S21, the SNR _{i at} the i-th (i = 1 to L) receiving antenna is It can be obtained by the following mathematical formula (3).

  Next, in the first wireless communication apparatus 302, the polarization-specific SNR estimation unit 50 ranks the SNRs for L in order of size, selects K antennas with large SNRs, and sends them to the combination pattern table unit 51. (S23). Here, K <L. Selecting an antenna element with a high SNR can be expected to increase the MIMO capacity, but it is also important to reduce the correlation between antennas as in the first embodiment. Therefore, in the third embodiment, a table that allows the combination pattern table unit 51 to select a combination of different polarizations so that the correlation of the remaining transmission antennas becomes low with respect to the combination of antennas selected in advance. Prepared, the transmission antenna selection unit 9 refers to this value, selects P antenna elements having a low correlation value as the remaining transmission antennas, and sends them to the transmission antenna control unit 10 (S24). Here, the conditions of P <L−K and P + K = M ′ are satisfied.

Next, in the first wireless communication apparatus 302, the transmission antenna selection unit 9 instructs the transmission antenna control unit 10 on information on the selected antenna, and the selected antenna and transmitters 2-1 to 2-M ′. Are switched by the transmission antenna control unit 10 (S25). Thereafter, the first wireless communication station 302 transmits the signals S _{1 to} S _{M ′} generated by the transmission signal generation unit 1 from the selected M ′ transmission antennas (S26). On the other hand, in the second radio communication station 200, the propagation channel estimation unit 15 estimates the propagation channel response (S27), and the decoding processing unit 16 decodes the received signal (S28).

  In the first to third embodiments described above, when p ≧ 2, first, K antennas are selected, and then one antenna having a small correlation with these K antennas is selected. It is also possible to set so that the correlation between the p antennas selected later is reduced by repeating the operation of selecting one antenna having a small correlation with the K + 1 antennas selected in (1). At the same time, it is also possible to select p antennas and obtain p antennas at a time so that the correlation of the entire K + p antennas becomes small.

D. Next, effects of the first to third embodiments described above will be described.
In the present invention, the number of antenna elements on the transmission side is 8, the number of antenna elements on the reception side is 4, and the number of transmitters is 3. That is, in this case, a signal can be transmitted from a maximum of three antennas. The maximum number of antennas selected is 3, and 3 × 4 MIMO transmission is performed as the MIMO channel. The element spacing between the antennas was 1 wavelength each. Since the algorithm on the decoding side is intended to be simplified as described above, the ZF method was used. The antenna polarization was all vertical polarization, and the array element spacing was one wavelength.

  For the evaluation, a signal format conforming to IEEE802.11a adopted in the wireless LAN was adopted. That is, the signal is an OFDM signal, the number of FFT (First Fourier Transform) points is 64, and the number of subcarriers is 52. The modulation method was fixed at 64QAM (Quadrature Amplitude Modulation) and R = 2/3, and the Bit Error Rate (BER) was obtained by changing the SNR. In order to realize MIMO transmission, the propagation channel response of a 4 × 8 MIMO channel was obtained by repeating the long preamble signal four times for propagation channel estimation. The propagation path is assumed to be a multiwave environment simulating an indoor environment.

In the present invention, two antennas having a high SNR are first selected, and six correlation values are calculated between the two and the remaining six, and the antenna in the combination having the lowest correlation is determined as the remaining one. Selected. On the other hand, in the technique according to the prior art, the channel capacity of Expression (1) is obtained from the propagation channel responses of all combinations ₈ C ₃ = 56, in which 3 elements are selected from 8 elements, and the transmission antenna is determined.

  FIG. 6 is a conceptual diagram showing the results of an evaluation test for comparing the performance of the wireless communication device according to the present invention and the wireless communication device according to the prior art. In FIG. 6, the present invention, the conventional method, and the selection of no transmission antenna are compared when the antenna interval is 1λ and three antennas are fixedly arranged. As is clear from the figure, in the present invention, for example, the required transmission power required to obtain BER = 10−3 is achieved despite the fact that the control for determining the transmission antenna is greatly improved compared to the conventional method. Is only a 0.5 dB increase. It can also be seen that the transmission power can be reduced to 4 dB when the number of transmission antenna elements is not selected.

  As described above, by using the present invention, high-quality MIMO transmission can be realized on the receiving side without using a complicated decoding method.

It is a block diagram which shows the structure of the radio | wireless communication apparatus by 1st Embodiment of this invention. 5 is a flowchart for explaining the operation of the wireless communication apparatus according to the first embodiment. It is a block diagram which shows the structure of the radio | wireless communication apparatus by 2nd Embodiment of this invention. It is a block diagram which shows the structure of the radio | wireless communication apparatus by 3rd Embodiment of this invention. 10 is a flowchart for explaining an operation of the wireless communication apparatus according to the third embodiment. It is a conceptual diagram which shows the result of the evaluation test for comparing the performance of the radio | wireless communication apparatus by this invention and the radio | wireless communication apparatus by a prior art. It is a block diagram which shows the structure of the radio | wireless communication apparatus by a prior art.

Explanation of symbols

1 Transmission signal generator 2-1 to 2-M transmitter (transmission means)
3-1 to 3-M circulator 4 switch 6-1 to 6-M receiver 7 propagation channel estimation unit (propagation channel estimation means)
9 Transmitting antenna selection section (second antenna selection means)
DESCRIPTION OF SYMBOLS 10 Transmission antenna control part 11 Propagation channel estimation signal transmission part 12-1 to 12-N Transmitter 13-1 to 13-N Circulator 14-1 to 14-N Receiver 15 Propagation channel estimation part 16 Decoding processing part 30 SNR Estimator (received power estimating means, first antenna selecting means, received power calculating means)
31 Correlation value calculation unit (correlation value calculation means)
40-1, 40-2 Signal processing unit 41 Inter-terminal correlation monitoring unit 50 SNR estimation unit by polarization 51 Combination pattern table unit 200 Wireless communication device (other wireless communication device, second wireless communication device)
300, 301, 302 Wireless communication device (first wireless communication device)
# 1 to #L antenna (first antenna group)
# 1 to #N Antenna (second antenna group)

Claims (6)

A MIMO channel including a first antenna group including four or more antennas, and including the first antenna group and a second antenna group including a plurality of antennas included in another wireless communication device. A wireless communication device for performing MIMO communication by spatially multiplexing a plurality of signal systems via the same frequency channel and the same time,
A reception power estimation means for estimating a reception power of each antenna of the first antenna group using a channel response value of a propagation path between the radio communication device and the other radio communication device;
First antenna selection means for selecting, from the first antenna group, a plurality of antennas having relatively large received power estimated by the received power estimation means;
Correlation value calculating means for calculating correlation values between a plurality of antennas selected by the first antenna selecting means and antennas other than the plurality of antennas;
Second antenna selection means for selecting at least one antenna other than the plurality of antennas from which the correlation value calculated by the correlation value calculation means becomes relatively small;
A wireless communication apparatus comprising: a transmission unit configured to transmit a signal using an antenna selected by the first antenna selection unit and the second antenna selection unit. The first antenna group includes L (L is an integer of 4 or more) antenna elements,
The second antenna group includes N antenna elements,
The received power estimating means includes
Propagation channel estimation means for estimating a propagation channel response transmitted from the other wireless communication device;
A reception power calculation unit that calculates reception power obtained by each of the L antenna elements based on the propagation channel response value estimated by the propagation channel estimation unit;
The first antenna selecting means selects K (K <L) antenna elements having relatively large received power calculated by the received power calculating means from the first antenna group,
The correlation value calculating means calculates (L−K) spatial correlations for each of the selected K antenna elements and (L−K) antenna elements,
The second antenna selection means selects P (P <LK) antenna elements having a relatively small spatial correlation value from among (LK) antenna elements. Item 2. The wireless communication device according to Item 1. Between the first wireless communication apparatus including a first antenna group including four or more antennas and the second wireless communication apparatus including a second antenna group including a plurality of antennas, the first A wireless communication method for performing MIMO communication by spatially multiplexing a plurality of signal systems at the same frequency channel and at the same time through a MIMO channel constituted by one antenna group and the second antenna group,
A first step of estimating received power for each of the first antennas using a channel response value of a propagation path between the first wireless communication device and the second wireless communication device;
A second step of selecting, from the first antenna group, a plurality of antennas having a relatively large estimated received power;
A third step of calculating a correlation value between the selected plurality of antennas and an antenna other than the plurality of antennas;
A fourth step of selecting at least one antenna other than the plurality of antennas for which the calculated correlation value is relatively small;
And a fifth step of transmitting a signal using a plurality of antennas having a relatively large received power and at least one antenna having a relatively small correlation value. The first antenna group includes L (L is an integer of 4 or more) antenna elements,
The second antenna group includes N antenna elements,
In the first step, a propagation channel response transmitted from the second wireless communication apparatus is estimated, and reception obtained by each of the L antenna elements based on the estimated propagation channel response value Calculate power,
In the second step, K (K <L) antenna elements having relatively large received power calculated by the received power calculating means are selected from the first antenna group,
In the third step, (L−K) spatial correlations are calculated for each of the selected K antenna elements and (L−K) antenna elements,
4. In the fourth step, P (P <L−K) antenna elements having a relatively small spatial correlation value are selected from (L−K) antenna elements. The wireless communication method described. The antenna element of the first wireless communication device is an antenna element having at least two different polarization characteristics,
A sixth step of measuring the received power of the antenna element for each polarization characteristic;
A seventh step of determining a combination of the antenna elements based on the polarization characteristics of the antenna elements;
And an eighth step of determining an antenna element to be used for transmission based on the received power of the antenna element measured for each polarization characteristic and the predetermined combination of the antenna elements. The wireless communication method according to claim 3 or 4 .   5. The wireless communication method according to claim 4, wherein when there are a plurality of the second wireless communication devices, the first to fifth steps are performed for each of the second wireless communication devices. .

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