JP4535292B2 - Wireless communication system - Google Patents

Description

  The present invention relates to a radio communication system to which a multiple input multiple output (MIMO) technique is applied.

  In recent years, a technology for transmitting a large amount of data at a limited frequency is required, and the MIMO technology is attracting attention as a method for realizing the technology. In addition, with regard to the MIMO technology, research for improving the communication capacity and BER (Bit Error Rate) has been actively conducted.

  In wireless communication systems that do not apply MIMO technology, the communication capacity C per Hz is known from Shannon's information theory.

(See Non-Patent Document 1).

  From the above equation, in order to improve the communication capacity per 1 Hz, it is necessary to increase the transmission power and the reception SNR (Signal to Noise Ratio). Therefore, there is a limit to reducing the power consumption of the wireless communication system. On the other hand, if the MIMO technology is applied, the communication capacity per 1 Hz can be improved by increasing the number of antennas without increasing the transmission power.

  However, even if the MIMO technology is applied, the communication capacity is not ideally improved. It has been confirmed that the actual communication capacity varies depending on the eigenvalue of the correlation matrix of the channel response matrix that represents the transfer characteristic (communication path environment) of the radio propagation path between the transmitting station and the receiving station.

  Hereinafter, the relationship between the communication capacity of a MIMO wireless communication system (hereinafter referred to as a MIMO communication system) to which this MIMO technology is applied and the eigenvalues of the correlation matrix of the channel response matrix will be described.

  For example, the communication capacity C per 1 Hz in the 2 × 2 MIMO communication system shown in FIG.

It becomes. Here, γ ₀ is the sum of reception SNRs at all reception antennas, and λ ₁ and λ ₂ indicate eigenvalues of the correlation matrix of the channel response matrix. However, λ ₁ ≧ λ ₂ .

When γ ₀ in the above formula (1) is a fixed value, from the relationship of (synergistic average) ≦ (arithmetic average)

And communication capacity C is

It is represented by Therefore, the communication capacity C becomes maximum when λ ₁ = λ ₂ .

  This relationship is not limited to the 2 × 2 MIMO communication system shown in FIG. 12 but also an M × N (M, N: arbitrary number) MIMO communication system. That is, in general, in the MIMO communication system, the communication capacity C is maximized when the eigenvalues of the correlation matrix of the channel response matrix are all equal. M is the number of transmission antennas provided in the transmission station, and N is the number of reception antennas provided in the reception station.

  Next, the communication capacity C when the communication path environment is good and when the communication path environment is bad will be examined. Specifically, it is assumed that the communication path environment is good when the eigenvalue variation of the correlation matrix of the channel response matrix is the smallest, and the communication path environment is poor when the eigenvalue variation is the largest.

First, a signal transmitted from the transmitting antenna 101 is t ₁ , a signal transmitted from the transmitting antenna 102 is t ₂ , a signal received by the receiving antenna 103 is r ₁ , and a signal received by the receiving antenna 104 is r _2. Then the relationship between these signals is

It is represented by here

Is the channel response matrix, n1, n ₂ is the Gaussian noise which appears in the received by the receiving antenna 103 and 104 signals.

According to Non-Patent Document 3, if the phase difference between h ₁₁ and h ₁₂ in equation (3) is θ ₁ , the phase difference between h ₂₁ and h ₂₂ is θ ₂ and φ = θ ₂ −θ _1.

In this case, even if the expression (3) is described as the following expression (4), generality is not lost.

  However,

The average value of is 1 and K is the carrier power.

At this time, the eigenvalues λ ₁ and λ ₂ of the correlation matrix are

Thus, when φ is changed from 0 ° to 180 °, the eigenvalues λ ₁ and λ ₂ change as shown in the graph of FIG.

As can be seen from the graph shown in FIG. 13, λ ₁ = λ ₂ = 1 when the variation in eigenvalue is the smallest, and λ ₁ = 2 and λ ₂ = 0 when the variation in eigenvalue is the largest.

When the communication path environment when λ ₁ = λ ₂ = 1 is type 1, and the communication path environment when λ ₁ = 2 and λ ₂ = 0 is type 2, communication in the type 1 and 2 communication path environments The characteristics of the capacitor C are shown in FIG.

As can be seen from the graph shown in FIG. 14, the communication capacity increases as the value of the received SNR increases. Further, the communication capacity of the type 1 communication path environment (λ ₁ = λ ₂ = 1) is larger than that of the type 2 communication path environment (λ ₁ = 2, λ ₂ = 0). Further, in the communication path environment (λ ₁ = λ ₂ = 1) when the variation of the eigenvalue is minimum and the communication path environment (λ ₁ = 2, λ ₂ = 0) when the variation of the eigenvalue is the maximum, reception is performed. As the SNR value increases, the difference in communication capacity increases.

  Next, the case of using QPSK (Quadrature Phase Shift Keying) as a modulation scheme will be considered for the BER of the 2 × 2 MIMO communication system shown in FIG.

From the above equation (4), the eigenvalues λ ₁ and λ ₂ of the correlation matrix are

Therefore, BER can be expressed by the following formula (5). Also, the BER characteristics at each φ are as shown in the graph of FIG.

  Note that γ is a CNR (carrier power to noise ratio) per receiving antenna.

As can be seen from the BER characteristics shown in FIG. 15, the BER is minimum when | φ | = 180. Further, the relationship between the eigenvalues λ ₁ and λ ₂ of the correlation matrix at this time is λ ₁ = λ ₂ .

  As described above, it has been shown that the communication capacity and the BER characteristics are significantly different between the communication path environment in which the eigenvalues of the correlation matrix of the channel response matrix vary and the communication path environment in which the channel response matrix does not vary.

  Therefore, various methods for improving communication capacity and BER have been studied in a wireless communication system to which MIMO technology is applied. Patent Document 1 describes an example thereof.

Patent Document 1 includes adaptive array antenna means that can change the directivity by changing the weights for a plurality of antenna elements. A matrix HH ^* (H represents a current channel response matrix, and H ^* represents its conjugate transpose matrix. The channel response matrix H ′ in which all eigenvalues are included within a predetermined range including the average value of the calculated eigenvalues, and the current channel response matrix H is calculated by the channel response matrix H It is described that the directivity of the adaptive array antenna means is adjusted so as to approach H ′ to improve the communication capacity of the communication path that can actually be used for communication.
JP 2005-045351 A Fukumura Ikuo, “Information Theory”, Corona, p. 253-254 Yoshio Karasawa, “MIMO propagation channel modeling”, IEICE Transactions B, vol. J86-B, no. 9, pp. 1706-1720, September 2003 Yutaka Murakami, Seiho Kobayashi, Masayuki Orihashi, Takeshi Matsuoka, “Analysis of BER characteristics using eigenvalues in MIMO system”, IEICE Technical Report, IT2002-76, ISEC2002-134, SST2002-182, ITS2002-159 (2003) 03)

  As described above, in the MIMO communication system, various methods for improving communication capacity and BER have been studied.

  The present invention has been made to solve the above-described problems of the prior art, and provides a MIMO wireless communication system capable of maximizing communication capacity and minimizing BER regardless of the communication path environment. The purpose is to provide.

In order to achieve the above object, a wireless communication system of the present invention includes a transmitting station that transmits signals using a plurality of transmitting antennas, and a receiving station that receives signals transmitted from the transmitting stations using a plurality of receiving antennas. An input multiple output wireless communication system,
The transmitting station is
In this configuration, the phase of each element of the channel response matrix is changed so that the minimum eigenvalue of the correlation matrix of the channel response matrix representing the channel environment between the transmitting station and the receiving station is maximized.

Or, having a transmitting station that transmits a signal with a plurality of transmitting antennas, and a receiving station that receives a signal transmitted from the transmitting station with a plurality of receiving antennas,
The transmitting station adds a required weight to a plurality of different signals and combines them, and then transmits the signals from a plurality of transmitting antennas, and the receiving station transmits signals from the transmitting station using a plurality of receiving antennas. A multi-input multi-output wireless communication system that performs maximum ratio combining and
The transmitting station is
In this configuration, the phase of each element of the channel response matrix is changed so that the maximum eigenvalue of the correlation matrix of the channel response matrix representing the channel environment between the transmitting station and the receiving station is maximized.

Alternatively, a transmitting station that transmits signals using a plurality of transmitting antennas, a receiving station that receives signals transmitted from the transmitting station using a plurality of receiving antennas, and a signal transmitted from the transmitting station to the receiving station are relayed. A wireless communication system of a multiple input multiple output system having a relay station,
The relay station is
The phase of each element of the first channel response matrix is changed so that the minimum eigenvalue of the correlation matrix of the first channel response matrix representing the communication path environment between the relay station and the receiving station is maximized. is there.

Alternatively, a transmitting station that transmits signals using a plurality of transmitting antennas, a receiving station that receives signals transmitted from the transmitting station using a plurality of receiving antennas, and a signal transmitted from the transmitting station to the receiving station are relayed. A relay station,
The transmitting station and the relay station add a required weight to a plurality of different signals and combine them, and then transmit from each of the plurality of transmitting antennas, and the receiving station receives a plurality of receiving antennas from the transmitting station. A multi-input multi-output wireless communication system that receives a transmitted signal and performs maximum ratio combining,
The relay station is
The phase of each element of the first channel response matrix is changed so that the maximum eigenvalue of the correlation matrix of the first channel response matrix representing the communication path environment between the relay station and the receiving station is maximized. is there.

  According to the present invention, a MIMO wireless communication system capable of maximizing communication capacity and minimizing BER can be obtained.

Next, the present invention will be described with reference to the drawings.
(First embodiment)
In the first embodiment, the transmission station equally divides the total transmission power and transmits signals from a plurality of transmission antennas, and the reception station receives signals transmitted from the transmission station by a plurality of reception antennas. This is an example suitable for the MIMO communication system shown in FIG. 1 (hereinafter referred to as a normal transmission MIMO communication system). 1 shows a configuration example in which a transmitting station transmits signals from two transmitting antennas 801 and 802, and a receiving station receives signals from two receiving antennas 803 and 804.

  The MIMO communication system according to the first embodiment includes a phase control device that multiplies a signal before transmission (a signal before IFFT processing) by a phase control matrix G in a transmission station, and a communication path between the transmission station and the reception station. A phase controller is used to change the phase of each element of the channel response matrix so that the minimum eigenvalue of the correlation matrix of the channel response matrix representing the environment is maximized. This maximizes the communication capacity of the normal transmission MIMO communication system shown in FIG. 1 and minimizes the BER. Hereinafter, a specific configuration and operation for that purpose will be described.

  First, the configuration of the MIMO communication system according to the first embodiment will be described using the 2 × 2 MIMO communication system shown in FIG. 2 as an example.

  As shown in FIG. 2, the MIMO communication system according to the first embodiment includes a transmission station 1203 including two transmission antennas 1201 and 1202, a phase control device 1204, a control unit 1208, and a storage unit 1209, The receiving station 1207 includes receiving antennas 1205 and 1206.

  The phase control device 1204 is for changing the phase of each element of the channel response matrix representing the communication path environment between the transmitting station 1203 and the receiving station 1207.

  The control unit 1208 controls the phase change amount of each element of the channel response matrix by the phase control device 1204. The phase control device 1204 and the control unit 1208 are, for example, a CPU or a DSP that executes processing according to a program, or a combination of these and analog processing circuits such as various logic circuits, A / D converters, and D / A converters. realizable.

  In general, a wireless base station device, a terminal device, and the like constituting a wireless communication system have functions as a transmitting station 1203 and a receiving station 1207, respectively. The receiving station 1207 uses a well-known method for the channel characteristics between the transmitting station and the receiving station in order to select an optimal transmission rate, modulation method, encoding method, or the like according to the state of the channel. And the function of notifying the measurement result (channel information) to the transmission side (transmission station 1203). In that case, the transmitting station 1203 may generate a channel response matrix based on the channel information, and may adjust the phase of each element of the generated channel response matrix. Note that when it is expected that the communication path environment will not fluctuate (such as communication between fixed terminal devices), the channel response matrix may be a fixed value set in advance.

  The storage unit 1209 is used to hold channel response matrix information set in advance and channel information transmitted from the receiving station 1207.

  The transmission station 1203 serial-parallel converts the signal before transmission to generate two systems of transmission signals. The phase control device 1204 multiplies the two transmission signals by a phase control matrix G for changing the respective phases. The transmission signal of one system multiplied by the phase control matrix G is transmitted from the transmission antenna 1201, and the transmission signal of the other system is transmitted from the transmission antenna 1202.

Signals transmitted from the transmission antennas 1201 and 1202 are received by the reception antennas 1205 and 1206 of the reception station 1207. At this time, the signal received by the receiving station 1207 is equivalent to the multiplication result of the signal transmitted from the transmitting station 1203 and the channel response matrix H ₁ representing the communication path environment between the transmitting station 1203 and the receiving station 1207. The phase control matrix G and the channel response matrix H ₁ are as shown in FIG.

And

Here, a signal transmitted from the transmission antenna 1201 is t ₁ , a signal transmitted from the transmission antenna 1202 is t ₂ , a signal received by the reception antenna 1205 is r ₁ , and a signal received by the reception antenna 1206 is r ₂ . Then the relationship between these signals is

It is represented by At this time

In other words, φ ₁ , φ ₂ , φ ₃ , and φ ₄ can be arbitrarily changed by changing θ ₁ , θ ₂ , θ ₃ , and θ ₄ .

Next, the eigenvalues of the correlation matrix of the channel response matrix H ₂ will be examined.

Reference 1 (Yoshio Karasawa, Tetsuki Taniguchi, Minami Zhang, “About Optimal Transmission of Maximum Ratio Combining Diversity OFDM in MIMO Configuration”, IEICE Technical Report, AP 2001-196, p. 45-52, 2002 -1), the eigenvalues λ ₁ and λ ₂ (λ ₁ ≧ λ ₂ ) of the correlation matrix of the channel response matrix H ₂ are expressed as follows.

However, ξ = φ ₁ + φ ₄ -φ ₂ -φ ₃ .

  A typical example is

Then,

become.

Subsequently, the communication capacity and BER when ξ is changed will be examined using the above formulas for λ ₁ and λ ₂ .

  The communication capacity C per 1 Hz in the MIMO communication system of the first embodiment is based on the above-mentioned Non-Patent Document 2, assuming that the sum of received SNRs at all receiving antennas is γ.

It becomes.

  FIG. 3 shows how the communication capacity characteristic changes with respect to ξ based on this equation.

  As shown in FIG. 3, the communication capacity C per 1 Hz is improved when ξ is increased, and is maximized when the absolute value of ξ is 180 °.

  On the other hand, the BER in the MIMO communication system according to the first embodiment is expressed by the following equation when QPSK is used as the modulation scheme.

  FIG. 4 shows how the BER characteristics change with respect to ξ based on this equation.

  As shown in FIG. 4, the BER decreases when ξ is increased, and becomes minimum when the absolute value of ξ is 180 °.

Therefore, if the phase θ ₁ , θ ₂ , θ ₃ , θ ₄ of the signal transmitted by the phase control device 1204 provided in the transmission station 1203 is changed and adjusted so that the absolute value of ξ becomes 180 °, the communication capacity Can be realized, and a MIMO communication system in which the BER is minimized can be realized.

  Next, the operation of the phase control apparatus 1204 provided in the transmission station 1203 of the first embodiment will be described with reference to FIG.

  As shown in FIG. 5, the phase control device 1204 includes phase controllers 1303 to 1306 that delay the transmission signals of the two systems, and adders 1307 and 1308 that add the signals output from the phase controllers 1303 to 1306. It has.

The transmission signal input from the data input terminal 1301 is branched into two. One of the branched signals is delayed in phase by θ ₁ by the phase controller 1303, and the other of the branched signals is delayed in phase by θ ₃ by the phase controller 1304.

Similarly, the transmission signal input from the data input terminal 1302 is branched into two, one of the branched signals is delayed in phase by θ ₂ by the phase controller 1305, and the other of the branched signals is the phase controller. 1306 delays the phase by θ ₄ .

The signal whose phase is delayed by θ _{1 by the} phase controller 1303 and the signal whose phase is delayed by θ _{2 by the} phase controller 1305 are added by the adder 1307 and output from the data output terminal 1309.

Similarly, a signal whose phase is delayed by θ ₂ by the phase controller 1304 and a signal whose phase is delayed by θ _{4 by the} phase controller 1306 are added by the adder 1308 and output from the data output terminal 1310.

The processing of the phase control device 1204 by the phase controllers 1303 to 1306 and the adders 1307 and 1308 is equivalent to the processing of multiplying the signal to be transmitted by the phase control matrix G and outputting it, and the phase of each element of the channel response matrix Equivalent to the process of changing. Therefore, according to the MIMO communication system of the present embodiment, the eigenvalues of the correlation matrix of the channel response matrix can be intentionally manipulated by the phase control device 1204. Therefore, if each phase θ ₁ , θ ₂ , θ ₃ , θ ₄ of the signal transmitted by the phase control device 1204 is changed and adjusted so that the absolute value of ξ becomes 180 °, the communication capacity is maximized, In addition, a MIMO communication system that minimizes the BER can be realized.

In the background art MIMO communication system described above, signals are transmitted and received without adjusting the eigenvalues of the correlation matrix of the channel response matrix. Therefore, the communication capacity and BER are determined depending on the communication path environment, and when the communication path environment is poor, the communication capacity is reduced and the BER is increased. On the other hand, in the MIMO communication system of the present embodiment, the MIMO communication system that maximizes the communication capacity and minimizes the BER in any channel environment by intentionally manipulating the eigenvalues of the correlation matrix of the channel response matrix. Can be realized.
(Second Embodiment)
In the MIMO communication system according to the second embodiment, a plurality of signals different depending on a transmitting station are added with a required weight and combined, then transmitted from a plurality of transmitting antennas, and received by a receiving station with a plurality of receiving antennas. This is a suitable example for the MIMO wireless communication system shown in FIG. 6 (hereinafter referred to as the maximum ratio combined transmission MIMO communication system) that receives a signal transmitted from a transmitting station and performs maximum ratio combining. FIG. 6 shows a configuration example in which a transmitting station transmits signals from two transmitting antennas 903 and 904, and a receiving station receives signals by two receiving antennas 905 and 906.

  As in the first embodiment, the MIMO communication system according to the second embodiment includes a phase control device that multiplies a signal before transmission (a signal before IFFT processing) by a phase control matrix G in the transmission station. The phase of each element of the channel response matrix is changed using the phase controller so that the maximum eigenvalue of the correlation matrix of the channel response matrix representing the channel environment between the transmitting station and the receiving station is maximized. This maximizes the communication capacity of the normal transmission MIMO communication system shown in FIG. 1 and minimizes the BER.

  Hereinafter, the MIMO communication system according to the second embodiment will be described using the 2 × 2 MIMO communication system shown in FIG. 2 as an example, as in the first embodiment.

The configuration of the MIMO communication system and the channel response matrix H ₁ and the phase control matrix G representing the communication path environment between the transmitting station 1203 and the receiving station 1207 are the same as those in the first embodiment, and the description thereof is omitted. To do.

In the MIMO communication system according to the second embodiment, a signal transmitted from the transmission antenna 1201 is t ₁ , a signal transmitted from the transmission antenna 1202 is t ₂ , a signal received by the reception antenna 1205 is r ₁ , and the reception antenna. the signal received when the r ₂ in 1206, the relationship between these signals

It is represented by At this time

Then, by changing θ ₁ , θ ₂ , θ ₃ , and θ ₄ , φ ₁ , φ ₂ , φ ₃ , and φ ₄ can be arbitrarily changed.

Further, according to the reference document 1, the eigenvalues λ ₁ and λ ₂ (λ ₁ ≧ λ ₂ ) of the correlation matrix of the channel response matrix H ₂ are expressed as follows.

However, ξ = φ ₁ + φ ₄ -φ ₂ -φ ₃ .

  A typical example is

Then,

become.

  Therefore, the communication capacity C per 1 Hz in the MIMO communication system according to the second embodiment is based on the above-mentioned Non-Patent Document 2, assuming that the sum of received SNRs at all receiving antennas is γ.

It becomes.

  FIG. 7 shows a change in communication capacity characteristics with respect to a change in ξ based on this equation.

  As shown in FIG. 7, the communication capacity C per 1 Hz is improved when ξ is reduced, and is maximized when the absolute value of ξ is 0 °.

  On the other hand, the BER in the MIMO communication system according to the second embodiment is expressed by the following equation when QPSK is used as the modulation scheme.

  FIG. 8 shows how the BER characteristics change with respect to ξ based on this equation.

  As shown in FIG. 8, the BER decreases when ξ is reduced and becomes minimum when the absolute value of ξ is 0 °.

Therefore, according to the MIMO communication system of the second embodiment, the absolute values of ξ are obtained by changing the phases θ ₁ , θ ₂ , θ ₃ , and θ ₄ of the signal transmitted by the phase control device 1204 provided in the transmission station 1203. If the value is adjusted to be 0 °, a MIMO communication system in which the communication capacity is maximum and the BER is minimum can be realized.

Since the configuration and operation of the phase control device 1204 provided in the transmission station 1203 of the second embodiment are the same as those of the first embodiment, description thereof is omitted here.
(Third embodiment)
The third embodiment is an example suitable for the normal transmission MIMO communication system shown in FIG.

  The MIMO communication system according to the third embodiment is configured to include a relay station that relays a signal transmitted from the transmission station to the reception station between the transmission station and the reception station. Similarly to the phase control apparatus shown in the first embodiment, the relay station multiplies the signal to be relayed by the phase control matrix G, and the communication path environment between the transmission station and the relay station and between the relay station and the reception station. The phase of each element of the channel response matrix is changed using the phase controller so that the minimum eigenvalue of the correlation matrix of each channel response matrix representing the maximum value is maximized. This maximizes the communication capacity of the normal transmission MIMO communication system and minimizes the BER. Hereinafter, a specific configuration and operation for that purpose will be described.

  First, the configuration of the MIMO communication system according to the third embodiment will be described using the 2 × 2 MIMO communication system shown in FIG. 9 as an example.

  As shown in FIG. 9, the MIMO communication system according to the third embodiment includes a transmitting station 403 having two transmitting antennas 401 and 402, a receiving station 411 having two receiving antennas 409 and 410, The relay station 408 includes two transmission antennas 404 and 405, a control unit 412, a storage unit 413, and two reception antennas 406 and 407.

  The relay station 408 includes a channel response matrix (first channel response matrix) that represents a communication path environment between the transmission station 403 and the relay station 408, and a channel response matrix (a channel response matrix that represents a communication path environment between the relay station 408 and the reception station 411). The phase of each element of the second channel response matrix) is changed.

  The control unit 412 controls the phase change amount of each element of each channel response matrix by the relay station 408. The control unit 412 can be realized, for example, by combining a CPU or DSP that executes processing according to a program, or analog processing circuits such as various logic circuits, A / D converters, and D / A converters. The relay station 408 includes a well-known wireless communication unit including a transmission unit and a reception unit, a CPU and a DSP that execute processing in accordance with a program, or various logic circuits, an A / D converter, a D / A converter, and the like. This can be realized by combining these analog processing circuits.

  In general, a wireless base station device, a terminal device, and the like constituting a wireless communication system have functions as a transmitting station 403, a relay station 408, and a receiving station 411, respectively. Also, the relay station 408 provides a well-known method for determining the channel characteristics between the transmission station 403 and the relay station 408 in order to select an optimal transmission rate, modulation scheme, encoding scheme, or the like according to the channel status. And a function of notifying the measurement result (channel information) to the transmission side (transmission station). Similarly, the receiving station 411 knows the channel characteristics between the relay station 408 and the receiving station 411 in order to select an optimal transmission rate, modulation scheme, encoding scheme, or the like according to the channel status. It has a function of measuring using a method and a function of notifying the transmission side (transmission station) of the measurement result (channel information). In that case, the relay station 408 may generate a channel response matrix between the transmission station 403 and the relay station 408 based on the channel information measured by itself, and may adjust the phase of each element of the generated channel response matrix. Further, the relay station 408 generates a channel response matrix between the relay station 408 and the receiving station 411 based on the channel information notified from the receiving station 411, and adjusts the phase of each element of the generated channel response matrix. Good. Note that when it is expected that the communication path environment will not fluctuate (such as communication between fixed terminal devices), the channel response matrix may be a fixed value set in advance.

  The storage unit 413 is used to hold channel response matrix information set in advance and channel information transmitted from the receiving station 411.

  The transmission station 403 transmits different transmission signals via the two transmission antennas 401 and 402.

The relay station 408 receives the signal transmitted from the transmission station 403 by the reception antennas 406 and 407. At this time, the signal received by the relay station 408 includes a signal transmitted from the transmission station 403, a channel response matrix (first channel response matrix) H ₁ representing a communication path environment between the transmission station 403 and the relay station 408, and Is equivalent to the multiplication result of.

  The relay station 408 multiplies the signals received by the reception antennas 404 and 405 by the phase control matrix G, and transmits the multiplication result from the transmission antennas 406 and 407.

The receiving station 411 receives the signals transmitted from the relay station 408 by the receiving antennas 409 and 410. At this time, the signal received by the receiving station 411 includes a signal transmitted from the relay station 408, a channel response matrix (second channel response matrix) H ₂ representing a communication path environment between the relay station 408 and the receiving station 411, and Is equivalent to the multiplication result of. The phase control matrix G and the channel response matrices H ₁ and H ₂ are as shown in FIG.

And

Here, a signal transmitted from the transmitting antenna 401 is t ₁ , a signal transmitted from the transmitting antenna 402 is t ₂ , a signal received by the receiving antenna 409 is r ₁ , and a signal received by the receiving antenna 410 is r ₂ . Then the relationship between these signals is

It is represented by At this time

Then, by changing θ ₁ , θ ₂ , θ ₃ , and θ ₄ , φ ₁ , φ ₂ , φ ₃ , and φ ₄ can be arbitrarily changed.

Next, the eigenvalue of the correlation matrix of the channel response matrix H ₃ between the transmitting station 403 and the receiving station 411 will be considered.

According to the reference document 1, eigenvalues λ ₁ and λ ₂ (λ ₁ ≧ λ ₂ ) of the correlation matrix of the channel response matrix H ₃ are expressed as follows.

However, ξ = φ ₁ + φ ₄ -φ ₂ -φ ₃ .

  A typical example is

Then,

It becomes.

The communication capacity and BER when ξ is changed will be examined using the above equations for λ ₁ and λ ₂ .

  The communication capacity C per 1 Hz in the MIMO communication system according to the third embodiment is based on Non-Patent Document 2 assuming that the sum of received SNRs at all receiving antennas is γ.

It becomes.

  Based on this equation, the characteristics of the communication capacity with respect to the change of ξ change as shown in the graph of FIG. 3 as in the first embodiment, and the communication capacity C per 1 Hz is improved by increasing ξ, Maximum when the absolute value of ξ is 180 °.

  On the other hand, the BER in the MIMO communication system according to the third embodiment is expressed by the following equation when QPSK is used as the modulation scheme.

  Based on this equation, the BER characteristic with respect to the change of ξ changes as shown in the graph of FIG. 4 as in the first embodiment. The BER decreases as ξ increases, and the absolute value of ξ becomes 180. Minimum at °.

Therefore, if each phase θ ₁ , θ ₂ , θ ₃ , θ ₄ of the signal relayed by the repeater 408 is changed and adjusted so that the absolute value of ξ becomes 180 °, the communication capacity is maximized, and A MIMO communication system in which the BER is minimized can be realized.

  Next, the operation of repeater 408 provided in the MIMO communication system according to the third embodiment will be described with reference to FIG.

  As shown in FIG. 10, the repeater 1204 includes phase controllers 503 to 506 that delay received signals of two systems, and adders 507 and 508 that add the signals output from the phase controllers 503 to 506. I have.

The signal received by the receiving antenna 501 is branched into two, one of the branched signals is delayed in phase by θ ₁ by the phase controller 503, and the other of the branched signals is phased by θ ₃ by the phase controller 504. Only delayed.

Similarly, the signal received by the receiving antenna 502 is branched into two, one of the branched signals is delayed in phase by θ ₃ by the phase controller 505, and the other of the branched signals is phase-shifted by the phase controller 506. Is delayed by θ ₄ .

The signal whose phase is delayed by θ _{1 by the} phase controller 503 and the signal whose phase is delayed by θ _{2 by the} phase controller 505 are added by the adder 507 and transmitted from the transmitting antenna 509.

Similarly, the signal whose phase is delayed by θ ₂ by the phase controller 504 and the signal whose phase is delayed by θ _{4 by the} phase controller 506 are added by the adder 508 and transmitted from the transmitting antenna 510.

The processing of the relay station 408 by the phase controllers 503 to 506 and the adders 507 and 508 is equivalent to the processing of multiplying the signal to be transmitted by the phase control matrix G and outputting it, and the phase of each element of the channel response matrix is changed. Equivalent to changing process. Therefore, according to the MIMO communication system of this embodiment, the relay station 408 can intentionally manipulate the eigenvalues of the correlation matrix of the channel response matrix. Therefore, if the phase θ ₁ , θ ₂ , θ ₃ , θ ₄ of the signal relayed by the relay station 408 is changed and adjusted so that the absolute value of ξ becomes 180 °, the communication capacity is maximized, and A MIMO communication system in which the BER is minimized can be realized.

In the above description, the channel response matrix (first channel response matrix) H _{1 in which the} relay station 408 represents the channel environment between the transmission station 403 and the relay station 408 and the channel environment between the relay station 408 and the reception station 411 are shown. In the above example, the phase of the signal to be relayed is adjusted by using the channel response matrix (second channel response matrix) H ₂ that represents the first channel response matrix H ₁ or the second channel. it may adjust the phase of the signal to be relayed response matrix) using one of H ₂ only.
(Fourth embodiment)
The fourth embodiment is an example suitable for the MIMO communication system of the maximum ratio combining transmission method shown in FIG.

  As in the third embodiment, the MIMO communication system of the fourth embodiment multiplies the signal relayed by the relay station by the phase control matrix G, and sets the communication path environment between the transmitting station and the receiving station. The phase of each element of the channel response matrix is changed so that the maximum eigenvalue of the correlation matrix of the channel response matrix to be expressed becomes maximum. This maximizes the communication capacity of the maximum ratio combined transmission MIMO communication system and minimizes the BER.

  The MIMO communication system according to the fourth embodiment will be described below using the 2 × 2 MIMO communication system shown in FIG. 9 as an example, as in the third embodiment.

The configuration of the MIMO communication system, the channel response matrix H ₁ representing the communication path environment between the transmission station 403 and the relay station 408, the channel response matrix H ₂ representing the communication path environment between the relay station 408 and the reception station 411, and phase control Since the matrix G is the same as that of the third embodiment, the description thereof is omitted.

In the MIMO communication system according to the fourth embodiment, the signal transmitted from the transmission antenna 401 is t ₁ , the signal transmitted from the transmission antenna 402 is t ₂ , the signal received by the reception antenna 409 is r ₁ , and the reception antenna. If the signal received at 410 is r ₂ , the relationship between these signals is

It is represented by At this time

Then, by changing θ ₁ , θ ₂ , θ ₃ , and θ ₄ , φ ₁ , φ ₂ , φ ₃ , and φ ₄ can be arbitrarily changed.

Further, according to the reference document 1, the eigenvalues λ ₁ and λ ₂ (λ ₁ ≧ λ ₂ ) of the correlation matrix of the channel response matrix H ₃ are expressed as follows.

However, ξ = φ ₁ + φ ₄ -φ ₂ -φ ₃ .

  A typical example is

Then,

become.

  Therefore, the communication capacity C per 1 Hz in the MIMO communication system of the fourth embodiment is based on the above-mentioned Non-Patent Document 2, assuming that the sum of received SNRs at all receiving antennas is γ.

It becomes.

  Based on this equation, the characteristics of the communication capacity with respect to the change of ξ change as shown in the graph of FIG. 7 as in the second embodiment, and the communication capacity C per 1 Hz is improved when ξ is reduced, Maximum when the absolute value of ξ is 0 °.

  On the other hand, the BER in the MIMO communication system according to the fourth embodiment is expressed by the following equation when QPSK is used as the modulation scheme.

  Based on this equation, the BER characteristic with respect to the change in ξ changes as shown in the graph of FIG. 8 as in the second embodiment. The BER decreases as ξ decreases, and the absolute value of ξ is 0. Minimum at °.

Therefore, according to the MIMO communication system of the fourth embodiment, the absolute value of ξ becomes 0 ° by changing each phase θ ₁ , θ ₂ , θ ₃ , θ ₄ of the signal relayed by the repeater 408. By adjusting as described above, it is possible to realize a MIMO communication system having the maximum communication capacity and the minimum BER.

Since the configuration and operation of the repeater 408 included in the MIMO communication system of the fourth embodiment are the same as those of the third embodiment, description thereof is omitted here.
(Fifth embodiment)
The fifth embodiment is an example suitable for the normal transmission MIMO communication system shown in FIG. However, in the MIMO communication system according to the fifth embodiment, power is distributed to each transmission antenna based on a well-known water injection theorem. The water injection theorem for power distribution is described in Reference Document 2 (Kazuyuki Ozaki, Akinori Nakajima, Fumiyuki Adachi, “Multiplex Throughput Characteristics of Eigenmode MIMO Using Turbo Coded HARQ,” IEICE Tech.).

  As in the first embodiment, the MIMO communication system according to the fifth embodiment includes a phase control device that multiplies a signal before transmission (a signal before IFFT processing) by a phase control matrix G in the transmission station. The phase of each element of the channel response matrix is changed using the phase controller so that the minimum eigenvalue of the correlation matrix of the channel response matrix representing the channel environment between the transmitting station and the receiving station is maximized. This maximizes the communication capacity of the normal transmission MIMO communication system and minimizes the BER. Hereinafter, a specific configuration and operation for that purpose will be described.

  First, the configuration of the MIMO communication system according to the fifth embodiment will be described using the 2 × 2 MIMO communication system shown in FIG. 11 as an example.

  As shown in FIG. 11, the MIMO communication system according to the fifth embodiment includes a transmission station 1503 including two transmission antennas 1501 and 1502 and a phase control device 1504, and two reception antennas 1505 and 1506. The receiving station 1507 is included.

  The transmission station 1503 serial-parallel converts the signal before transmission to generate two systems of transmission signals. The phase control device 1504 multiplies the two transmission signals by a phase control matrix G for changing the respective phases. The transmission signal of one system multiplied by the phase control matrix G is transmitted from the transmission antenna 1501, and the transmission signal of the other system is transmitted from the transmission antenna 1502.

Signals transmitted from the transmission antennas 1501 and 1502 are received by the reception antennas 1505 and 1506 of the reception station 1507. At this time, the signal received by the receiving station 1507 is equivalent to the multiplication result of the signal transmitted from the transmitting station 1503 and the channel response matrix H ₁ representing the communication path environment between the transmitting station 1503 and the receiving station 1507. The phase control matrix G and the channel response matrix H ₁ are as shown in FIG.

And

Here, a signal transmitted from the transmitting antenna 1501 is t ₁ , a signal transmitted from the transmitting antenna 1502 is t ₂ , a signal received by the receiving antenna 1505 is r ₁ , and a signal received by the receiving antenna 1506 is r ₂ . Then the relationship between these signals is

It is represented by here

After all,

It becomes.

Next, the eigenvalues of the correlation matrix of the channel response matrix H ₂ will be examined.

According to the reference document 1, eigenvalues λ ₁ and λ ₂ (λ ₁ ≧ λ ₂ ) of the correlation matrix of the channel response matrix H ₂ are expressed as follows.

However, ξ = θ ₁₁ + θ ₂₂ −θ ₁₂ −θ ₂₁ + θ ₁ + θ ₄ −θ ₂ −θ ₃ .

  A typical example is

Then,

It becomes.

The communication capacity and BER when ξ is changed will be examined using the above equations for λ ₁ and λ ₂ .

  The communication capacity C per 1 Hz in the MIMO communication system according to the fifth embodiment is based on Non-Patent Document 2 given that the sum of received SNRs at all receiving antennas is γ.

It becomes.

  Based on this equation, the characteristics of the communication capacity with respect to the change of ξ change as shown in the graph of FIG. 3 as in the first embodiment, and the communication capacity C per 1 Hz is improved by increasing ξ, Maximum when the absolute value of ξ is 180 °.

  On the other hand, the BER in the MIMO communication system according to the third embodiment is expressed by the following equation when QPSK is used as the modulation scheme.

  Based on this equation, the BER characteristic with respect to the change of ξ changes as shown in the graph of FIG. 4 as in the first embodiment. The BER decreases as ξ increases, and the absolute value of ξ becomes 180 Minimum at °.

Therefore, according to the MIMO communication system of the fifth embodiment, each phase θ ₁ , θ ₂ , θ ₃ , θ ₄ of the signal transmitted by the phase control device 1504 provided in the transmission station 1503 is changed to obtain the absolute value of ξ. If the value is adjusted to be 180 °, a MIMO communication system in which the communication capacity is maximized and the BER is minimized can be realized.

Since the configuration and operation of the phase control device 1504 provided in the transmission station 1503 of the fifth embodiment are the same as those of the first embodiment, description thereof is omitted here.
(Sixth embodiment)
The sixth embodiment is an example suitable for the maximum ratio combining transmission scheme MIMO communication system shown in FIG. However, also in the MIMO communication system of the sixth embodiment, it is assumed that power is distributed to each transmission antenna based on a well-known water injection theorem, as in the fifth embodiment.

  As in the first embodiment, the MIMO communication system according to the sixth embodiment includes a phase control device that multiplies a signal before transmission (a signal before IFFT processing) by a phase control matrix G in the transmission station. The phase of each element of the channel response matrix is changed using the phase controller so that the maximum eigenvalue of the correlation matrix of the channel response matrix representing the channel environment between the transmitting station and the receiving station is maximized. Thereby, the communication capacity of the MIMO communication system of the maximum ratio combining transmission method shown in FIG. 6 is maximized and the BER is minimized. Hereinafter, a specific configuration and operation for that purpose will be described.

  The MIMO communication system according to the sixth embodiment will be described below using the 2 × 2 MIMO communication system shown in FIG. 11 as an example, as in the fifth embodiment.

Note that the configuration of the MIMO communication system and the channel response matrix H ₁ and the phase control matrix G representing the communication path environment between the transmitting station 1503 and the receiving station 1507 are the same as those in the fifth embodiment, and thus description thereof is omitted. To do.

In the MIMO communication system according to the sixth embodiment, the signal transmitted from the transmission antenna 1501 is t ₁ , the signal transmitted from the transmission antenna 1502 is t ₂ , the signal received by the reception antenna 1505 is r ₁ , and the reception antenna. If the signal received at 1506 is r ₂ , the relationship between these signals is

It is represented by here

After all,

It becomes.

Further, according to the reference document 1, the eigenvalues λ ₁ and λ ₂ (λ ₁ ≧ λ ₂ ) of the correlation matrix of the channel response matrix H ₂ are expressed as follows.

However, ξ = θ ₁₁ + θ ₂₂ −θ ₁₂ −θ ₂₁ + θ ₁ + θ ₄ −θ ₂ −θ ₃ .

  A typical example is

Then,

become.

  Therefore, the communication capacity C per 1 Hz in the MIMO communication system according to the sixth embodiment is based on Non-Patent Document 2 assuming that the sum of received SNRs at all receiving antennas is γ.

It becomes.

  Based on this equation, the characteristics of the communication capacity with respect to the change of ξ change as shown in the graph of FIG. 7 as in the second embodiment, and the communication capacity C per 1 Hz is improved when ξ is reduced, Maximum when the absolute value of ξ is 0 °.

  On the other hand, the BER in the MIMO communication system according to the sixth embodiment is expressed by the following equation when QPSK is used as the modulation scheme.

  Based on this equation, the BER characteristic with respect to the change in ξ changes as shown in the graph of FIG. 8 as in the second embodiment. The BER decreases as ξ decreases, and the absolute value of ξ is 0. Minimum at °.

Therefore, according to the MIMO communication system of the sixth embodiment, the absolute value of ξ becomes 0 ° by changing each phase θ ₁ , θ ₂ , θ ₃ , θ ₄ of the signal relayed by the repeater 408. By adjusting as described above, it is possible to realize a MIMO communication system having the maximum communication capacity and the minimum BER.

  Since the configuration and operation of the phase control device 1504 provided in the transmission station 1503 of the sixth embodiment are the same as those of the first embodiment, description thereof is omitted here.

  In the above-described first to sixth embodiments, the configuration, operation, and effect of the present invention have been described using the 2 × 2 MIMO communication system as an example. However, the present invention is not limited to M × N (M, N : Arbitrary number) Even when applied to a MIMO communication system, the same effects as those of the 2 × 2 MIMO communication system shown in the first to sixth embodiments can be obtained. M is the number of transmission antennas provided in the transmission station, and N is the number of reception antennas provided in the reception station.

It is a block diagram which shows the example of 1 structure of the MIMO communication system of the normal transmission system to which this invention is applied. It is a block diagram which shows the example of 1 structure of the MIMO communication system of 1st Embodiment. It is a graph which shows the change of the characteristic of communication capacity with respect to the change of (xi) of the MIMO communication system of 1st Embodiment. It is a graph which shows the change of the characteristic of BER with respect to the change of (xi) of the MIMO communication system of 1st Embodiment. FIG. 3 is a block diagram illustrating a configuration example of a phase control device provided in the transmission station illustrated in FIG. 2. It is a block diagram which shows one structural example of the MIMO communication system of the maximum ratio synthetic | combination transmission system to which this invention is applied. It is a graph which shows the change of the characteristic of communication capacity with respect to the change of (xi) of the MIMO communication system of 2nd Embodiment. It is a graph which shows the change of the characteristic of BER with respect to the change of (xi) of the MIMO communication system of 2nd Embodiment. It is a block diagram which shows the example of 1 structure of the MIMO communication system of 3rd Embodiment. FIG. 10 is a block diagram illustrating a configuration example of a relay station included in the MIMO communication system illustrated in FIG. 9. It is a block diagram which shows the example of 1 structure of the MIMO communication system of 5th Embodiment. It is a block diagram which shows the structure of a 2 * 2 MIMO communication system. It is a graph which shows the mode of the eigenvalue (lambda) ₁ and (lambda) ₂ change with respect to the change of (phi) in the MIMO communication system of background art. It is a graph which shows the characteristic of the communication capacity in a communication channel environment when the variation of an eigenvalue is the smallest, and a communication channel environment when the variation of an eigenvalue is the largest. It is a graph which shows the change of the characteristic of BER with respect to the change of (phi) of the MIMO communication system of background art.

Explanation of symbols

401, 402, 406, 407, 501, 502, 801, 802, 903, 904, 1201, 1201, 1501, 1502 Transmitting antenna 403, 1203, 1503 Transmitting station 404, 405, 409, 410, 509, 510, 803, 804, 905, 906, 1205, 1206, 1505, 1506 Receiving antenna 408 Relay station 411, 1207, 1507 Receiving station 412, 1208 Control unit 413, 1209 Storage unit 503-506, 1303-1306 Phase controller 507, 508, 1307 1308 Adder 1204, 1504 Phase controller 1301, 1302 Data input terminal 1309, 1310 Data output terminal

Claims (22)

A multi-input multi-output radio communication system having a transmitting station that transmits signals with a plurality of transmitting antennas and a receiving station that receives signals transmitted from the transmitting stations with a plurality of receiving antennas,
The transmitting station is
A wireless communication system that changes a phase of each element of the channel response matrix so that a minimum eigenvalue of a correlation matrix of a channel response matrix representing a communication path environment between the transmitting station and the receiving station is maximized. The transmitting station is
The wireless communication system according to claim 1, wherein information on the channel response matrix set in advance is held. The receiving station is
Measuring the characteristics of the communication path between the transmitting station and the receiving station, transmitting channel information for generating the channel response matrix obtained from the measurement result to the transmitting station;
The transmitting station is
The wireless communication system according to claim 1, wherein the phase of each element of the channel response matrix is changed based on the channel information. The transmitting station is
The radio communication system according to claim 1, wherein the signal is transmitted to a plurality of transmission antennas by equally dividing the total transmission power. The transmitting station is
The wireless communication system according to claim 1, wherein the signal is transmitted by allocating total transmission power to the plurality of transmission antennas based on a water injection theorem. A transmitting station that transmits signals with a plurality of transmitting antennas, and a receiving station that receives signals transmitted from the transmitting stations with a plurality of receiving antennas,
The transmitting station adds a required weight to a plurality of different signals and combines them, and then transmits the signals from a plurality of transmitting antennas, and the receiving station transmits signals from the transmitting station using a plurality of receiving antennas. A multi-input multi-output wireless communication system that performs maximum ratio combining and
The transmitting station is
A wireless communication system that changes a phase of each element of the channel response matrix so that a maximum eigenvalue of a correlation matrix of a channel response matrix representing a communication path environment between the transmitting station and the receiving station is maximized. The transmitting station is
The wireless communication system according to claim 6, wherein information on the preset channel response matrix is retained. The receiving station is
Measuring the characteristics of the communication path between the transmitting station and the receiving station, transmitting channel information for generating the channel response matrix obtained from the measurement result to the transmitting station;
The transmitting station is
The wireless communication system according to claim 6, wherein the phase of each element of the channel response matrix is changed based on the channel information. A transmitting station that transmits signals with a plurality of transmitting antennas, a receiving station that receives signals transmitted from the transmitting station with a plurality of receiving antennas, and a relay station that relays signals transmitted from the transmitting station to the receiving station A multi-input multi-output wireless communication system,
The relay station is
Wireless communication in which the phase of each element of the first channel response matrix is changed so that the minimum eigenvalue of the correlation matrix of the first channel response matrix representing the channel environment between the relay station and the receiving station is maximized system. The relay station is
The phase of each element of the second channel response matrix is changed so that a minimum eigenvalue of a correlation matrix of a second channel response matrix representing a channel environment between the transmitting station and the relay station is maximized. 9. The wireless communication system according to 9. The relay station is
The wireless communication system according to claim 9, wherein information on the first channel response matrix set in advance is held. The relay station is
The wireless communication system according to claim 10, wherein information on the second channel response matrix set in advance is held. The receiving station is
Measuring characteristics of a communication path between the relay station and the receiving station, and transmitting channel information for generating the first channel response matrix obtained from the measurement result to the relay station;
The relay station is
The wireless communication system according to claim 9, wherein the phase of each element of the first channel response matrix is changed based on the channel information. The relay station is
Measuring channel characteristics between the transmitting station and the relay station, obtaining channel information for generating the second channel response matrix obtained from the measurement result,
The wireless communication system according to claim 10, wherein the phase of each element of the second channel response matrix is changed based on the channel information. The relay station is
The wireless communication system according to claim 9, wherein the signal is transmitted to a plurality of transmission antennas by equally dividing the total transmission power. The relay station is
The wireless communication system according to claim 9, wherein the signal is transmitted by allocating total transmission power to a plurality of transmission antennas based on a water injection theorem. A transmitting station that transmits signals with a plurality of transmitting antennas, a receiving station that receives signals transmitted from the transmitting station with a plurality of receiving antennas, and a relay station that relays signals transmitted from the transmitting station to the receiving station And
The transmitting station and the relay station add a required weight to a plurality of different signals and combine them, and then transmit from each of the plurality of transmitting antennas, and the receiving station receives a plurality of receiving antennas from the transmitting station. A multi-input multi-output wireless communication system that receives a transmitted signal and performs maximum ratio combining,
The relay station is
Wireless communication in which the phase of each element of the first channel response matrix is changed so that the maximum eigenvalue of the correlation matrix of the first channel response matrix representing the channel environment between the relay station and the receiving station is maximized system. The relay station is
The phase of each element of the second channel response matrix is changed so that a maximum eigenvalue of a correlation matrix of a second channel response matrix representing a communication path environment between the transmitting station and the relay station is maximized. 17. The wireless communication system according to 17. The relay station is
The wireless communication system according to claim 17, wherein information of the first channel response matrix set in advance is held. The relay station is
The wireless communication system according to claim 18, wherein information on the second channel response matrix set in advance is held. The receiving station is
Measuring characteristics of a communication path between the relay station and the receiving station, and transmitting channel information for generating the first channel response matrix obtained from the measurement result to the relay station;
The relay station is
The wireless communication system according to claim 17, wherein the phase of each element of the first channel response matrix is changed based on the channel information. The relay station is
Measuring channel characteristics between the transmitting station and the relay station, obtaining channel information for generating the second channel response matrix obtained from the measurement result,
The wireless communication system according to claim 18, wherein the phase of each element of the second channel response matrix is changed based on the channel information.

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