KR20070032553A - Apparatus and method for phase rotation of antenna in mimo systems - Google Patents

Abstract

An apparatus and a method for rotating the phases of Tx antennas in a multi-antenna system are provided to improve the performance of an ML(Maximum Likelihood) receiver by executing phase rotation for each Tx antenna according to a Tx antenna phase rotation request signal and maximizing the minimum Euclidean distance. An apparatus for rotating the phases of Tx antennas in a multi-antenna system comprises a phase rotation angle confirmer(323), a phase rotation angle determiner(321), and multipliers(303,304). The phase rotation angle confirmer(323), if a Tx antenna phase rotation request signal is received, confirms the phase rotation state of each Tx antenna. The phase rotation angle determiner(321) determines a phase rotation angle for each Tx antenna according to the phase rotation state of each Tx antenna, the number of Tx antennas, and a modulation type. The multipliers(303,304) rotate the phases of the Tx antennas at the determined angles.

Description

Apparatus and method for phase rotation of a transmitting antenna in a multi-antenna system {APPARATUS AND METHOD FOR PHASE ROTATION OF ANTENNA IN MIMO SYSTEMS}

1 is a diagram illustrating a multi-antenna system using space-time block codes according to the prior art;

2 is a diagram illustrating signal constellations of a general multi-antenna system;

3 illustrates a multiple antenna system for performing phase rotation in accordance with the present invention;

4 is a diagram illustrating a procedure for performing rotation of a transmission antenna in a multiple antenna system according to an embodiment of the present invention;

5 is a diagram illustrating a procedure for requesting phase rotation according to channel correlation of a transmitting antenna in a multiple antenna system according to an embodiment of the present invention;

6 is a diagram illustrating a Euclidean distance when two transmitting antennas are used in a multi-antenna system according to an embodiment of the present invention; and

7 is a diagram illustrating a Euclidean distance when there are three transmit antennas in a multi-antenna system according to an exemplary embodiment of the present invention.

The present invention relates to an apparatus and a method for rotating a phase of a transmission antenna in a multiple antenna system (hereinafter referred to as MIMO), and in particular, to an Euclidean distance of signals received in the multiple antenna system. An apparatus and a method for rotating the phase of the transmitting antenna to maximize.

In the next generation wireless communication system, various technologies for transmitting more data with faster and lower error probability have been studied in order to support high quality multimedia service in a conventional voice service-oriented mobile communication system.

MIMO technology is recently attracting much attention as a system using multiple antennas for each of the transmitting and receiving ends, and compared to a system using a single antenna, the channel transmission capacity can be increased in proportion to the number of antennas without additional frequency or transmission power allocation.

In the MIMO Spatial Division Multiplexing (SDM), which transmits different transmission streams to multiple transmit antennas among the MIMO systems, when the number of transmit antennas is larger than the number of receive antennas, in case of an asymmetric structure, the influence of mutual interference between transmitted data is affected. In consideration, the maximum likelihood (hereinafter referred to as ML) series receiver is used. For example, the ML receiver includes an ML receiver, a successive interference cancellation (SIC), a vertical-bell lab layered space time (V-BLAST), and the like.

The performance of the ML receiver is proportional to the Euclidean distance of the signals received through the MIMO channel from all transmit antennas. However, when the correlation of the quasi-static MIMO channel is large in indoor or short-range wireless communication, the Euclidean distance of the received signals continues to decrease so that the performance of the ML receiver is degraded. Therefore, research to reduce the correlation of the channels are in progress.

1 illustrates a multiple antenna system using space-time block code according to the prior art.

As shown in FIG. 1, the transmitter of the multi-antenna system includes a space-time block code (hereinafter referred to as STBC) encoder 101 and a phase rotator 103, and the receiver includes a space-time block decoder ( 105).

First, the transmitter encodes and outputs a transmission signal from the STBC encoder 101. The phase rotor 103 rotates and modulates the coded signal provided from the STBC encoder 101 by θ, and then transmits the same through the transmitting antennas.

Since the signal received through the receiving antenna is a signal rotated by θ, the receiver decodes the STBC decoder 105 using the signal constellation point rotated by θ. Here, θ is a value that maximizes the average encoding gain of STBC. For example, if a QAM (Quadrature Amplitude Modulation) symbol is x _i , the signal point rotated by θ is represented by Equation 1 below.

Here, the modulation and demodulation is performed under the assumption that both transmitters and receivers are known at a predetermined rotation angle.

In addition, when the signal to noise ratio is high, the coding gain of the space-time code is proportional to a determinant metric as shown in Equation 2 below.

Where N _R represents the number of reception antennas, r and λ _k represent the coefficients and k-th eigenvalues for the space-time code matrix.

Accordingly, the transmitter calculates a rotation angle θ that maximizes the average value of the determinant calculation using Equation 3 for all possible STBC matrices so that the average encoding gain is maximized.

If the transmission antenna is 3 and QPSK (Quadrature Phase Shift Keying) modulation, the rotation angle θ is atan (1/3).

As described above, since the prior art uses the coding gain of the space-time code to rotate the signaling point, the optimal rotation angle can be obtained only when STBC is used in the open loop. Therefore, the optimal rotation angle cannot be obtained in the ML receiver of the general MIMO SDM system. In addition, both the transmitter and the receiver should be aware of the rotation angle of the fixed signaling point, and there is a problem that performance deterioration occurs when the correlation of the MIMO channel is large.

Accordingly, an object of the present invention is to provide an apparatus and method for obtaining a phase rotation angle for each transmitting antenna that maximizes the Euclidean distance scale of a received signal in a multi-antenna system.

Another object of the present invention is to provide an apparatus and method for improving the performance of a maximum likelihood receiver by setting an optimal phase angle according to the number of transmission antennas and a modulation scheme in a multiple antenna system.

According to a first aspect of the present invention for achieving the above objects, a transmission apparatus for rotating a phase of a transmission antenna in a multi-antenna system, when a phase rotation request signal is received, a phase for checking the phase rotation state of the transmission antennas A phase rotation angle determiner determining a phase rotation angle of the transmission antennas according to a rotation confirmer, a phase rotation state of the transmission antennas, the number and modulation scheme of the transmission antennas, and a phase rotation angle determined by the phase rotation angle determiner. And a multiplier for rotating the phases of the transmitting antennas.

According to a second aspect of the present invention, a receiving apparatus for rotating a phase of a transmitting antenna in a multi-antenna system includes a channel estimator for estimating a channel using a signal received from a transmitter, and the estimated channel information using the estimated channel information. And a phase rotation request determiner for detecting a correlation between channels and determining a phase rotation request of the transmitting antennas.

According to a third aspect of the present invention, a reception method for rotating a phase of a transmission antenna in a multi-antenna system includes, when a signal is received from a transmitter, estimating a channel using the received signal, and the estimated channel value. Calculating a correlation value of each channel by using a second value and comparing the absolute value of the difference between the channel correlation value and the first reference value with a threshold value; and the absolute value of the difference between the channel correlation value and the first reference value is the threshold value. If less than the value, characterized in that it comprises the step of transmitting a phase rotation request signal.

According to a fourth aspect of the present invention, a reception method for rotating a phase of a transmission antenna in a multi-antenna system includes, when a signal is received from a transmitter, estimating a channel using the received signal, and the estimated channel value. Calculating a correlation value of each channel by using a second value and comparing the absolute value of the difference between the channel correlation value and the first reference value with a threshold value; and the absolute value of the difference between the channel correlation value and the first reference value is determined by the threshold value. If less than the value, characterized in that it comprises the step of transmitting a phase rotation request signal.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Hereinafter, the present invention describes a technique for maximizing the Euclidean distance measure of received signals by rotating a phase of a transmitting antenna in a multiple antenna system (hereinafter referred to as MIMO). In the following description, the MIMO system is a MIMO SDI (Spatial Division Multiplexing) system of quasi-static channels such as indoor or near-field wireless communication.

Respectively through the N _T transmit antennas in the MIMO SDM system Q-QAM is to transmit the modulated signal ML (Maximum Likelihood: hereinafter, ML quot;) in the side of the receiver Q ^M of signals through the first transmit antenna constellations It is equivalent to transmitting a signal modulated randomly by the MIMO channel with a dot. For example, when two transmit antennas transmit a quadrature phase shift keying (QPSK) modulated signal 203 as shown in FIG. 2, the ML receiver has 16 (2 ⁴ ) random signals modified by the MIMO channel. Recognize it as a constellation point 205.

In this case, when the receiver assumes that the channel H is known, the symbol error of the ML estimation for the transmission symbol vector x is given by Equation 4 below.

Where E _s represents symbol energy, N ₀ represents variance of noise, and d _min (│Hx-Hx`│) represents the minimum Euclidean distance between received signaling points.

Therefore, as the d _min of FIG. 2 increases, the performance of the ML receiver is improved. Since d _min of the random signaling point 205 has a high probability of decreasing as the correlation between the channels increases, d _min becomes larger when the correlation value of the channel in the quasi-static channel continues to be small. There is a need for a device that changes phase.

 In general, the correlation may be measured as a correlation value for the magnitude of the channel coefficient between transmitting antennas. However, in the present invention, it is assumed that the magnitude of the channel coefficients between the transmitting antennas in the quasi-static fading channel is almost the same.

φ _i and φ _j represent phase rotation angles of the transmission antennas, and h _i and h _j represent phase angles of the transmission antennas.

If the difference between the phase difference φ _ij and the reference phase difference between the i th transmit antenna and the j th transmit antenna is less than or equal to the threshold value T in Equation 5, the probability that d _min becomes small increases, so phase rotation is requested. Here, the reference phase difference means a phase difference that minimizes d _min . For example, if you have two transmit antennas and use square QAM modulation (eg QPSK, 16QAM, 64QAM), the reference phase difference is given in multiples of 2 / π.

3 shows a multiple antenna system for performing phase rotation in accordance with the present invention. The following description takes an example of a transmitter having three transmit antennas.

As shown in FIG. 3, the transmitter includes a MUX 301, a multipliers 303 and 304, and a phase controller 305. The receiver includes an ML decoder 311, a channel estimator 313, and a phase detector 315. It is configured to include.

First, the transmitter multiplexes the transmission signals by the number of transmission antennas (eg, three) in the MUX 301 and outputs the multiplexed signals. The multipliers 303 and 304 phase rotate the transmission signal provided from the MUX 301 according to the phase rotation angle provided from the phase controller 305 and transmit the transmission signal through each transmission antenna.

The phase controller 305 includes a phase rotation angle determiner 321 and a phase rotation angle checker 323, and controls the phase of the transmission signal to maximize the minimum Euclidean distance d _min . When the phase rotation request signal is received from the receiver, the phase rotation angle checker 323 checks the phase rotation angles of the current transmission antennas according to the phase rotation angle information of the transmission antennas provided by the phase rotation angle determiner 321. do. That is, it is checked whether the current transmitting antennas are in phase rotated state.

The phase rotation angle determiner 321 determines the phase rotation angles of the transmission antennas according to the phase rotation state of the current transmission antenna provided from the phase rotation angle identifier 323. That is, if the current transmitting antennas do not have phase rotation (θ ₁ , θ ₂ , θ ₃ = 0), the phase rotation angle corresponding to the transmitter is selected from a predetermined phase rotation angle table according to the number of transmitting antennas and the modulation scheme. To the multipliers 303 and 304.

If the current transmission antenna is rotated at an arbitrary phase rotation angle, the phase rotation angle determiner 321 sets the phase rotation angle of the transmission antenna to 0 and provides the multipliers 303 and 304.

Next, the ML decoder 311 at the receiver detects a signal received through the reception antenna. The channel estimator 313 estimates a channel using the pilot signal of the received signal and provides the channel to the ML decoder 311 and the phase detector 315. The phase detector 315 calculates a channel correlation value of each transmitting antenna using the channel information provided from the channel estimator 313. In this case, the channel correlation value is measured based on the phase difference of the channel coefficients on the assumption that the magnitudes of the channel coefficients between the transmitting antennas are almost the same in the quasi-static fading channel.

If the calculated channel correlation value is less than the reference phase difference, the phase controller 305 transmits a phase rotation request signal. Here, the phase rotation request signal transmits a signal of 1 bit when the phase rotation request is received.

4 illustrates a procedure for performing rotation of a transmission antenna in a multi-antenna system according to an exemplary embodiment of the present invention.

Referring to FIG. 4, first, the transmitter transmits a signal to the receiver in step 401, and the transmitter proceeds to step 403 to determine whether a phase rotation request signal is received from the receiver. The phase rotation request signal is a 1-bit feedback signal.

If the phase rotation request signal is received, the transmitter proceeds to step 405 and the phase rotation angle checker 323 confirms the phase rotation state of the current transmitting antennas. If the transmitting antennas are not in phase rotation, the transmitter proceeds to step 407 to select a phase rotation angle of the transmitter using a predetermined phase rotation table according to the number of transmitting antennas and a modulation scheme. Thereafter, the transmitter proceeds to step 409 to rotate the transmit antennas according to the selected phase rotation angle, and the transmitter proceeds to step 411 to transmit a signal at the rotated phase angle. The transmitter then terminates this algorithm.

If the transmitting antennas are in phase rotation, the transmitter proceeds to step 413 to select the phase rotation angle of the transmitting antennas as zero. Thereafter, the transmitter proceeds to step 409 to rotate the transmit antennas according to the selected phase rotation angle, and then the transmitter proceeds to step 411 to transmit a signal at the rotated phase angle. The transmitter then terminates this algorithm.

5 illustrates a procedure for requesting phase rotation according to channel correlation of a transmitting antenna in a multi-antenna system according to an exemplary embodiment of the present invention.

Referring to FIG. 5, when a signal is received from the transmitter in step 501, the receiver proceeds to step 503 to estimate a channel using a pilot of the received signal.

In operation 505, the receiver measures channel correlation values of respective transmission antennas using the estimated channel value. In this case, the channel correlation value is measured based on the phase difference of the channel coefficients on the assumption that the magnitudes of the channel coefficients between the transmitting antennas are almost the same in the quasi-static fading channel. In addition, the channel correlation value measurement is performed periodically.

After measuring the channel correlation value, the receiver proceeds to step 507 in which the absolute value (| φ _ij -φ |) of the difference between the measured channel correlation value φ _ij and the reference phase difference φ is determined as the threshold value ( Compare to T). If the absolute value of the difference between the channel correlation value and the reference phase difference is greater than or equal to the threshold value (| φ _ij -φ | ≥ T), the receiver returns to step 501 and returns the channel correlation value of the next received signal. Check.

If the absolute value of the difference between the channel correlation value and the reference phase difference is smaller than the threshold value (| φ _ij -φ | <T), the receiver proceeds to step 509 and transmits a phase rotation request signal to the transmitter. . The phase rotation request signal is a 1-bit feedback signal. That is, if there is a phase rotation request, a feedback signal of 1 bit is transmitted, and if there is no phase rotation request, no signal is transmitted.

The receiver then terminates this algorithm.

6 and 7 illustrate an optimal Euclidean distance according to the number of transmitting antennas in a multi-antenna system according to an embodiment of the present invention. In the following description, FIG. 6 shows a case of using two transmit antennas, and FIG. 7 shows a case of using three transmit antennas.

First, as illustrated in FIG. 6, the horizontal axis represents a phase rotation angle, and the vertical axis represents a Euclidean distance. Here, since only one transmit antenna needs to be rotated based on one transmit antenna among two transmit antennas, only one phase rotation angle is shown.

 6A illustrates a change in Euclidean distance according to the phase rotation angle when using QPSK, and FIG. 6B illustrates a change in Euclidean distance according to the phase rotation angle when using 16QAM.

Next, as shown in FIG. 7, the horizontal axis represents the phase rotation angle of the second antenna, and the vertical axis represents the phase rotation angle of the third antenna.

FIG. 7A illustrates the change in Euclidean distance according to the phase rotation angle when BPSK is used, and FIG. 7B illustrates the change in Euclidean distance according to the phase rotation angle when QPSK is used.

In this case, when the correlation between the channel coefficients is high and the powers from all transmitting antennas are the same, and the phase difference between the channel coefficients of the remaining antennas with respect to the channel coefficients of the first transmitting antennas is close to zero, the phase rotation angle for each transmitting antenna Euclidean distance according to is calculated as shown in Equation 6.

Here, d _min represents the minimum Euclidean distance, θ _i represents a phase rotation angle of the i-th transmit antenna, x _n denotes a transmission signal of the n th antenna.

When the optimum phase rotation angle is calculated by using Equation 6, it is shown in Tables 1 and 2.

Modulation method Reference phase difference (φ) Phase rotation angle set (θ ₁ , θ ₂ ) BPSK 0, π (0, π / 3), (0, 2π / 3) QPSK 0, π / 2, π. 3π / 2 (0, π / 6), (0, π / 3), (0, 2π / 3), (0, 5π / 6) 16QAM 0, π / 2, π, 3π / 2 (0, π / 12), (0, π / 6), (0, π / 3), (0, 2π / 3), (0, 5π / 6, (0, 11π)

Here, Table 2 shows a reference phase difference and a set of phase rotation angles for each transmitting antenna when two transmitting antennas are used.

Modulation method Reference phase difference (φ) Phase rotation angle set (θ ₁ , θ ₂ , θ ₃ ) BPSK 0, π / 3, 2π / 3, π, 4π / 3 (0, π / 5, 2π / 5), (0, π / 5, 4π / 5), (0, 3π / 5, 4π / 5) QPSK` 0, π / 6, π / 3, π / 2, 2π / 3, 5π / 6, π, 7π / 6, 4π / 3, 3π / 2, 5π / 3, 11π / 6 (0, π / 10, π / 5), (0, π / 10, 2π / 5), (0, π / 10, 7π / 10), (0, π / 5, 3π / 5), (0 , 3π / 10, 2π / 5), (0, 3π / 10, 9π / 10), (0, 2π / 5, 3π / 5), (0, 2π / 5, 4π / 5), (0, 3π / 5, 7π / 10), (0, 3π / 5, 9π / 10), (0, 4π / 5, 9π / 10)

Here, Table 2 shows a reference phase difference and a set of phase rotation angles for each transmitting antenna when three transmitting antennas are used.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, in the MIMO SDM system of the quasi-static fading channel, when the transmitting antenna phase rotation request signal is received, as the phase rotation for each transmitting antenna is performed, even when a large correlation value of the channel continues, The maximum likelihood receiver can be improved by maximizing the minimum Euclidean distance through phase rotation of each transmitting antenna. In addition, since only the phase is rotated for each transmission antenna, the complexity of the transmitter is low and the overhead is reduced because the phase rotation request signal of 1 bit is fed back only when the channel correlation value exceeds the threshold.

Claims (17)

In the transmitting apparatus for rotating the phase of the transmitting antenna in a multi-antenna system, A phase rotation checker for checking a phase rotation state of the transmitting antennas when a phase rotation request signal is received; A phase rotation angle determiner for determining phase rotation angles of the transmission antennas according to a phase rotation state of the transmission antennas, the number of modulation antennas, and a modulation scheme; And a multiplier for rotating the phases of the transmit antennas at a phase rotation angle determined by the phase rotation angle determiner. The method of claim 1, The phase rotation checker, And receiving phase rotation angle information of the transmitting antennas from the phase rotation angle determiner and checking the phase rotation state of the transmitting antennas. The method of claim 1, The phase rotation angle determiner, If the transmit antennas are in a phase rotated state, the phase rotation angle of the transmit antennas is determined as 0, And if the transmit antennas are not in phase rotation, selecting a phase rotation angle of the transmit antennas from a predetermined table according to the number of transmit antennas and a modulation scheme. The method of claim 1, And the phase rotation request signal is a 1-bit feedback signal. A receiving apparatus for requesting rotation of a phase of a transmitting antenna in a multi-antenna system, A channel estimator for estimating a channel using a signal received from a transmitter, And a phase rotation request determiner for detecting a correlation between channels using the estimated channel information to determine a phase rotation request of transmission antennas. The method of claim 5, And the channel correlation value calculates a phase difference of a channel coefficient between the transmitting antennas as a scale. The method of claim 5, The phase rotation request determiner, Comparing the absolute value of the difference between the channel correlation value and the first reference value and a predetermined threshold, and transmitting a phase rotation request signal when the absolute value of the difference between the channel correlation value and the first reference value is smaller than the threshold value. Device characterized in that. The method of claim 7, wherein And the phase rotation request signal uses a 1-bit feedback signal. The method of claim 7, wherein And wherein the first reference value is a reference phase difference that minimizes the minimum Euclidean distance. In the transmission method for rotating the phase of the transmission antenna in a multi-antenna system, Checking a phase rotation state of the transmitting antennas when a phase rotation request signal is received; Selecting phase rotation angles of the transmission antennas from the predetermined table if the transmission antennas are not in phase rotation; And transmitting a signal by rotating a phase of the transmitting antennas using the selected phase rotation angle. The method of claim 10, The predetermined table is characterized in that the phase rotation angle is determined and stored in accordance with the number of the transmission antenna and the modulation scheme in advance. The method of claim 10, If the transmitting antennas are in a phase rotated state, determining a phase rotation angle of the transmitting antennas as 0. The method of claim 10, And the phase rotation request signal is a 1-bit feedback signal. A reception method for requesting rotation of a phase of a transmission antenna in a multi-antenna system, Estimating a channel using the received signal when a signal is received from a transmitter, Calculating a correlation value of each channel by using the estimated channel value and comparing an absolute value of a difference between the channel correlation value and a first reference value with a threshold value; And transmitting a phase rotation request signal when the absolute value of the difference between the channel correlation value and the first reference value is smaller than the threshold value. The method of claim 14, The channel correlation value is characterized by using the phase difference of the channel coefficient between the transmitting antennas as a measure. The method of claim 14, And wherein the first reference value is a reference phase difference that minimizes the minimum Euclidean distance. The method of claim 14, The phase rotation request signal is characterized in that for using a 1-bit feedback signal.

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