KR101508426B1 - Pre-coding apparatus and method in open loop multiple input multiple output system - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multiple input multiple output (MIMO) system, and more particularly, to a multiple input multiple output (MIMO) system in which a channel environment is not fed back from a receiver, The present invention relates to a precoding apparatus and method in an open loop multi-antenna system capable of preventing degradation in performance, and more particularly, to a precoding apparatus and method in an open loop multi- (Or "pre-coding") a transmission signal separated by a code, it is possible to prevent deterioration of reception performance of a transmission signal in a channel without lowering the feedback error of the receiver, thereby lowering the system error probability (PEP) It is possible to reduce the complexity and overhead of the system.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pre-coding apparatus and method for an open-

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multiple input multiple output (MIMO) system, and more particularly, to a multiple input multiple output (MIMO) system in which a channel environment is not received from a receiver To an apparatus and method for precoding in an open-loop multi-antenna system capable of preventing performance deterioration of a signal.

2. Description of the Related Art In recent years, studies have been actively made on a multiple input multiple output (MIMO) system having an effect of improving reception performance and increasing data transmission capacity.

In particular, MIMO has been removed from the use of a single transmission antenna and a single input single output (SISO) so far, and multiplexing of spatial and spatial multiplexing (hereinafter referred to as "spatial multiplexing Spatial Multiplexing "), thereby improving the transmission efficiency of the transmission / reception data and increasing the data transmission capacity.

 The spatial multiplexing performance of such a MIMO system results in severe reception performance degradation due to correlation of channels between transmit antennas.

In order to prevent deterioration in the performance of such a received signal, the receiver estimates the channel environment from the signal received through the spatial multiplexing channel, feeds back the estimated channel environment information to the transmitter, reflects the channel environment to the transmission signal, Is applied.

The feedback MIMO system is composed of a transmitter having a plurality of transmit antennas and a receiver having a plurality of receive antennas.

1 is a diagram showing a configuration of a general feedback type MIMO system applying a codebook method.

Referring to FIG. 1, a codebook MIMO system is a system in which a transmitter 10 selects codebook sets designed in advance in a codebook storage unit 13 and then precodes the transmission signals separated by the precoding application unit 11 The receiver 10 receives the transmission signal to which the precoding is applied, estimates the channel environment from the reception signal through the channel estimation unit 22, and optimizes the channel environment for various channel environments Selects a codeword corresponding to the estimated channel environment through the codeword selector 23 storing the codewords of the codeword, and transmits the selected codeword to the transmitter 10 via the feedback channel. At this time, the transmitter 10 searches the codebook corresponding to the code index received via the feedback channel from the codebook 13, and outputs the code word to the precoding application unit 11. The precoding application unit 11 applies the code word To the separated transmission signals for transmission through the transmission antennas of the transmission unit 12, and transmits the transmission signals through the corresponding antenna of the transmission unit 12. The channel estimation and codeword selection techniques are self-evident techniques to those skilled in the art, and thus a detailed description thereof will be omitted.

 2 is a diagram illustrating a configuration of a general feedback type MIMO system applying a rotation transformation technique.

2, the MIMO system using the rotation transformation technique calculates a correlation coefficient from the channel environment information estimated through the channel estimation unit 22 of the receiver 20, and transmits the calculated correlation coefficient to a transmitter The transmitter 10 includes a correlation coefficient calculation unit 24 that calculates a correlation coefficient based on a rotation conversion scheme, a power allocation scheme, and a system based on a representative matrix, based on a correlation coefficient received from the correlation coefficient calculation unit 24, And a rotation conversion unit 14 for calculating parameter values of precoding for minimizing the error and outputting the pre-code to which the calculated parameter values are applied, to the precoding application unit 11. [ The correlation coefficient calculation method, the rotation conversion method, and the method of calculating the precoding parameter value for minimizing the system error by the power allocation and matrix are obvious to those having ordinary skill in the art, and detailed description will be omitted.

As described above, the MIMO channel environment is estimated from the transmission signal transmitted from the transmitter, and the estimated channel environment information is fed back to the transmitter, thereby preventing channel performance deterioration due to spatial multiplexing.

However, the MIMO system of the feedback scheme has a high complexity.

Also, there is a problem that performance degradation occurs due to a feedback error in a broadcasting system which is an open loop system or a system having a fast fading channel environment in which feedback information is difficult to receive.

Accordingly, there is a demand for a method for preventing performance deterioration of a received signal due to spatial multiplexing in an open loop MIMO system such as a system having a broadcast system and a fast fading channel environment.

Therefore, it is an object of the present invention to provide a precoding apparatus and a precoding apparatus in an open-loop multi-antenna system capable of preventing deterioration of performance of a received signal in an open-loop transmit correlation fine fading channel in which feedback of a channel environment is not received from a receiver, Method.

In order to achieve the above object, the precoding apparatus in an open loop multiple antenna system of the present invention includes: a receiver for receiving a transmission signal transmitted through a plurality of reception antennas including at least two reception antennas through the reception antennas; And a receiver including a signal combining and demodulating unit for combining and demodulating the received signals and outputting the demodulated signals, the transmitter comprising: a transmitter for transmitting spatially multiplexed transmission signals including at least two transmission antennas; A modulation section for modulating and outputting the separated signals; a pre-code matrix section having a pre-code matrix for the number of transmission antennas; Environment to minimize the system error, A pre-code unit for determining a component (?,?) Of a column and determining an optimal pre-code by applying the determined component, and a pre-code unit for applying the determined pre-code to the separated and modulated signals output from the modulator And a pre-coding application unit for outputting the pre-coding application to the transmission unit.

The modulator is one of a QPSK modulator for performing QPSK modulation on the input signals and a 16QAM modulator for performing 16-QAM modulation on the input signals.

And the number of the transmission antennas and the number of the reception antennas is two.

The pre-code matrix unit may include a rotation matrix and a phase rotation matrix as shown in Equation (1).

[Equation 1]

The pre-code unit determines the component of the pre-code matrix minimizing the system average error probability (PEP) according to Equation (2) to minimize the system error assumed to be the worst channel environment.

&Quot; (2) "

)는 변조 차수에 따른 코드워드의 차이다. (이 때 코드워드의 차는 변조 차수에 따라 다르며, BPSK, 16-QAM, 64-QAM, M-QAM을 각각 적용 할 수 있음).Here, M is the modulation order, N _t is the number of transmit antennas, Nr is the number of receive antennas, r is the signal-to-noise ratio (SNR) and, R _t is transmitted correlation matrix, F is a pre-code matrix, (

) Is the difference in codeword according to modulation order. (In this case, the difference of the codeword differs depending on the modulation order, and BPSK, 16-QAM, 64-QAM, and M-QAM can be applied respectively.

According to another aspect of the present invention, there is provided a precoding method in an open-loop multi-antenna system including: a transmitter including at least two transmit antennas of an open-loop multi-antenna system including a receiver including at least two receive antennas; A pre-code matrix component determining step of determining a component (?,?) Of the pre-code matrix that loads a pre-code matrix for the number of transmit antennas and assumes a worst case channel environment and minimizes a system error; A pre-code determining step of determining a pre-code by applying a pre-code matrix component to a pre-code matrix; a signal separating step of separating a signal to be transmitted so as to correspond to the number of transmission antennas; And outputting the separated and modulated signals output from the modulator to the determined Applying a code to re-apply the pre-code output process in the transmitter, and the signal is applied to the pre-code, it characterized in that it comprises a transmission step of transmitting over a respective transmit antenna.

Wherein the modulation is one of QPSK modulation for performing QPSK modulation on the input signals and 16-QAM modulation for performing 16-QAM modulation on the input signals.

When the number of transmit and receive antennas is 2, the pre-code matrix is composed of a rotation matrix and a phase rotation matrix as shown in Equation (1).

[Equation 1]

The pre-code section determines the component (?,?) Of the pre-code matrix minimizing the system average error probability (PEP) according to Equation (2) to minimize the system error assumed to be the worst channel environment .

&Quot; (2) "

)는 변조 차수에 따른 코드워드의 차이다. Here, M is the modulation order, N _t is the number of transmit antennas, Nr is the number of receive antennas, r is the signal-to-noise ratio (SNR) and, R _t is transmitted correlation matrix, F is a pre-code matrix, (

) Is the difference in codeword according to modulation order.

(Or "precoding") a transmission signal separated by a precode considering the worst channel environment that can prevent the deterioration of the average reception signal performance, assuming that the transmission correlation coefficient is the worst It is possible to prevent deterioration of the performance of the received signal in the channel and to reduce the Pairwise Error Probability (PEP) according to the feedback information.

Further, since the present invention does not have a feedback structure, it has the effect of reducing the complexity and overhead of the system.

1 is a diagram showing a configuration of a general feedback type MIMO system applying a codebook method.
2 is a diagram illustrating a configuration of a general feedback type MIMO system applying a rotation transformation technique.
3 is a diagram illustrating a configuration of an open-loop multi-antenna system including a precoding apparatus according to the present invention.
FIG. 4 is a flowchart illustrating a precoding method in a precoding apparatus of an open-loop multi-antenna system according to the present invention.
5 is a graph showing reception performance according to a correlation coefficient without phase due to the pre-coding of the present invention.
6 is a graph showing an average reception performance according to a signal-to-noise ratio when a correlation coefficient by the pre-coding of the present invention is 1 and a phase exists in a normal distribution.
FIG. 7 is a graph illustrating a reception performance according to a phase with a correlation coefficient of 1 according to the pre-coding according to the present invention.

Hereinafter, a configuration and operation of a precoding apparatus in an open-loop multi-antenna system according to the present invention will be described with reference to the accompanying drawings, and a coding method in the apparatus will be described.

3 is a diagram illustrating a configuration of an open-loop multi-antenna system including a precoding apparatus according to the present invention.

The open loop multi-antenna system according to the present invention includes a transmitter 100 and a receiver 20 according to the present invention.

The open loop multi-antenna system transmitter 100 according to the present invention includes a signal separator 110, a modulator 120, a pre-code matrix unit 150, a pre-code unit 160, a precoding application unit 130, And a transmission unit 140.

The signal separator 110 separates a transmission signal to be transmitted into a number corresponding to the number of transmission antennas and outputs the separated transmission signal.

The modulator 120 modulates and outputs each of the transmission signals separated by the signal separator 110 according to a predetermined modulation scheme. The modulation scheme may be a quadrature phase shift keying (QPSK) scheme. BPSK, 16-QAM, 64-QAM, M-QAM, 8-PSK, 16-PSK, M-PSK All the modulation methods of the baseband can be applied.

The pre-code matrix unit 150 stores a pre-code matrix including a rotation matrix and a phase rotation matrix as shown in Equation (1).

The matrix of free codes for the number of transmit antennas is based on a combination of a rotation matrix and a phase rotation matrix. In this case, when the correlation coefficient of the channel is 0 and precoding is applied, performance degradation does not occur since the pre-code matrix has orthogonal characteristics.

For example, when a 2x2 matrix, i.e., a transmit antenna and a receive antenna, is configured, the precoding matrix may be expressed as Equation (1) below, where each component of the precoding matrix, The phase of the matrix is the phase value of the rotation matrix, and the phase is the phase rotation matrix. [theta] and [phi] may be derived by the following equation (2) and the experimental method.

[Equation 1]

In Equation (1), the first item is a rotation matrix and the second item is a phase rotation matrix.

The pre-code unit 160 determines an optimal pre-code for minimizing a system error and outputs the pre-code based on a worst-case channel environment.

을 이용하여 시스템 오류를 최소화 하는 최적의 θ와 φ 변수를 결정하고, 결정된 θ와 φ를 상기 수학식 1에 적용하여 프리 코드를 결정한다.More specifically, the pre-code unit 160 sets a phase variable value of each component of the pre-code matrix of the pre-code matrix unit 150 as a transmission correlation coefficient (having a value between 0 and 1, 1) is set to 1 and the average PEP of Equation (2) is adjusted to the modulation order,

To determine optimal θ and φ parameters that minimizes the system error, and determines the pre-code by applying the determined θ and φ to Equation 1 above.

&Quot; (2) "

)는 변조 차수에 따른 코드워드의 차이다. Here, M is the modulation order, N _t is the number of transmit antennas, Nr is the number of receive antennas, r is the signal-to-noise ratio (SNR) and, R _t is transmitted correlation matrix, F is a pre-code matrix, (

) Is the difference in codeword according to modulation order.

For example, if the number of transmission antennas is 2, the modulation method is QPSK, and the parameter determined by Equation 2 is θ = π / 8φ = π / 4 based on Equation 1, Is determined according to the following equation (3).

&Quot; (3) "

If the 2 × 2 matrix, ie, the number of transmit antennas is 2 and the modulation method is 16-QAM, and the parameter determined by Equation 2 is θ = π / 8 φ = π / 4 based on Equation 1, Is determined according to the following equation (4).

&Quot; (4) "

The precoding application unit 130 applies the precoded code to the separated and modulated transmission signals output from the modulation unit 120, and outputs the precoded code to the transmission unit 140.

The transmission unit 140 transmits the precoded encoded transmission signals through the respective transmission antennas.

The receiver 20 includes a reception unit 21 having a number of reception antennas corresponding to the number of transmission antennas of the transmission unit 140 and receiving and outputting the orthogonal precoded transmission signals transmitted from the transmitter 100, And a signal combining and demodulating unit 23 for modulating a transmission signal (hereinafter referred to as "reception signal" The receiver 20 according to the present invention is constructed in the same manner as the conventional receiver, and transmits a signal assuming a worst channel environment. Therefore, feedback information such as a channel estimation, a codeword selector, a correlation coefficient calculator, It is not necessary to provide a configuration for providing the information.

FIG. 4 is a flowchart illustrating a precoding method in a precoding apparatus of an open-loop multi-antenna system according to the present invention. This will be described below with reference to Figs. 3 to 4. Fig.

First, the pre-code unit 160 loads a pre-code matrix from the pre-code matrix unit 150, and minimizes a system error based on the retrieved phase variable values, assuming the worst channel environment, i.e., The component values?,? Are determined (S411).

When the component value is determined, the pre-code unit 160 applies the component value to the pre-code matrix to determine an optimal pre-code (S413).

When an optimal precode is determined and a signal to be transmitted is generated, the signal separator 110 separates the signal to be transmitted to correspond to the number of transmission antennas (S415) and modulates the separated transmission signal (S417).

When the transmission signal is separated and modulated and outputted, the pre-code applying unit 130 performs complex-prime coding on the separated and modulated transmission signals output from the modulator 120 by applying the determined pre-code to transmit signals, 140 (S419).

The transmitter 140 transmits the complex pre-coded input signals through the corresponding transmit antenna at step S421.

FIG. 5 is a graph illustrating reception performance according to the correlation coefficient without phase by the pre-coding of the present invention.

Referring to FIG. 5, a phase rotation matrix is constructed by a complex matrix having a complex value of a pre-code matrix, and the phase values of the pre-code complex matrix are orthogonalized as described with reference to FIGS. 3 and 4, The performance degradation of the received signal does not occur even when it is zero.

As shown in FIG. 5, as the correlation coefficient increases, the performance of the reception signal 501 that does not perform precoding is rapidly degraded.

However, it can be seen that the transmission signal 503 that has undergone precoding according to the present invention exhibits a relatively constant reception performance.

The transmission signal 503 that has undergone precoding according to the present invention is substantially similar to the performance of the transmission signal 502 that receives the feedback information and performs precoding even though the feedback information is not received from the receiver 20 .

6 is a graph showing an average reception performance according to a signal-to-noise ratio when a correlation coefficient by the pre-coding of the present invention is 1 and a phase exists in a normal distribution.

Referring to FIG. 6, a signal-to-noise ratio (SNR) 603 of a transmission signal of the present invention is a ratio of a signal-to-noise ratio 601 of a transmission signal that has not been precoded to a signal- 602). ≪ / RTI >

FIG. 7 is a graph illustrating a reception performance according to a phase with a correlation coefficient of 1 according to the pre-coding according to the present invention.

Referring to FIG. 7, a signal-to-noise ratio (SER) 702 of a transmission signal according to the present invention is indicated by reference numeral 701. The signal-to-noise ratio 703 of a transmission signal that has not been precoded, Is better than the signal-to-noise ratio 704 that performs precoding based on the signal-to-noise ratio.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. It will be easily understood. It is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, it is intended to cover various modifications within the scope of the appended claims.

10: Transmitter 11: Precoding application section
12: Transmission unit 13: Codebook storage unit
14: rotation converter 20: receiver
21: Receiver 22: Channel estimator
23: signal combining and demodulating unit 24: correlation coefficient calculating unit
100: Transmitter 110: Signal separation unit
120: Modulation part 130: Precoding application part
140: Transmitting section 150: Pre-code matrix section
160:

Claims (12)

And a receiver including a receiver including at least two reception antennas for receiving a transmission signal transmitted through the reception antennas and a signal combining and demodulating unit for combining signals received through the receiver, A transmitter of a loop multi-antenna system,
Comprising: a transmitter for transmitting spatially multiplexed transmission signals including at least two transmission antennas;
A signal separator for separating a signal to be transmitted so as to correspond to the number of transmission antennas,
A modulator for modulating and outputting the separated signals,
A pre-code matrix unit having a pre-code matrix composed of a rotation matrix and a phase rotation matrix with respect to the number of transmission antennas,
A precode unit for determining a component (?,?) Of the pre-code matrix that minimizes a system error on the assumption of a worst channel environment and determining an optimal precode by applying the determined component;
And a precoding applying unit for applying the determined pre-code to the transmitting unit, and outputting the separated and modulated signals output from the modulating unit to the transmitting unit.
The method according to claim 1,
Wherein the modulator comprises:
A QPSK modulator for performing QPSK modulation on the input signals and outputting the QPSK signals; and a 16QAM modulator for performing 16-QAM modulation on the input signals to output the modulated signals. .
The method according to claim 1,
Wherein the number of transmit antennas and the number of receive antennas are two.
The method of claim 3,
The pre-
The apparatus of any preceding claim, wherein the transmitter comprises a rotation matrix and a phase rotation matrix as shown in Equation (1).
[Equation 1]

3. The method of claim 2,
Wherein the number of transmit antennas and the number of receive antennas are two.
6. The method of claim 5,
The pre-
The apparatus of any preceding claim, wherein the transmitter comprises a rotation matrix and a phase rotation matrix as shown in Equation (1).
[Equation 1]

The method according to claim 6,
The pre-
Characterized in that said component of a pre-code matrix which minimizes a system average error probability (PEP) is determined by the following equation (2) in order to minimize a system error assumed to be the worst channel environment: .
&Quot; (2) "

Here, M is the modulation order, N _t is the number of transmit antennas, Nr is the number of receive antennas, r is the signal-to-noise ratio (SNR) and, R _t is transmitted correlation matrix, F is a pre-code matrix, (

) Is the difference in codeword according to modulation order.
A transmitter having at least two transmit antennas of an open-loop multi-antenna system including a receiver including at least two receive antennas,
A pre-code matrix composed of a rotation matrix and a phase rotation matrix with respect to the number of transmission antennas is loaded and a component of the pre-code matrix that minimizes a system error by assuming a worst- θ, Φ) of the pre-code matrix,
A pre-code determining step of determining a pre-code by applying the determined pre-code matrix component to a pre-
A signal separating step of separating a signal to be transmitted so as to correspond to the number of transmission antennas,
A signal modulating step of modulating and outputting the separated signals,
A pre-code applying step of applying separated and modulated signals output from the modulating unit to the transmitting unit by applying the determined pre-code,
And transmitting the signals to which the pre-code is applied through the respective transmit antennas.
9. The method of claim 8,
The modulation may comprise:
Wherein the input signal is one of QPSK modulation for performing QPSK modulation on the input signals and 16-QAM modulation for performing 16-QAM modulation on the input signals.
9. The method of claim 8,
Wherein when the number of the transmission antennas and the number of the reception antennas is two, the pre-code matrix is composed of a rotation matrix and a phase rotation matrix as shown in Equation (1) A method for predicting a system transmitter.
[Equation 1]

10. The method of claim 9,
Wherein when the number of the transmission antennas and the number of the reception antennas is two, the pre-code matrix is composed of a rotation matrix and a phase rotation matrix as shown in Equation (1) A method for predicting a system transmitter.
[Equation 1]

12. The method of claim 11,
The pre-
(?,?) Of the pre-code matrix minimizing the system average error probability (PEP) is determined by the following equation (2) to minimize the system error assumed to be the worst channel environment: A pre - coding method of a loop multi - antenna system transmitter.
&Quot; (2) "

Here, M is the modulation order, N _t is the number of transmit antennas, Nr is the number of receive antennas, r is the signal-to-noise ratio (SNR) and, R _t is transmitted correlation matrix, F is a pre-code matrix, (

) Is the difference in codeword according to modulation order.

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