KR20140057902A - Method and apparatus of successive interference cancellation detection in mulitiple inuput multiple output antenna system - Google Patents

Abstract

The present invention relates to wireless communications and, more in detail, to a method and an apparatus for detecting successive interference cancellation (SIC) in a multi-input and multi-output antenna system. The method of the present invention comprises the steps of: receiving a MIMO transmission signal; detecting a transmission symbol including a channel noise component; decoding the transmission symbol including the channel noise component and acquiring bit information; detecting the SIC based on the bit information; inserting a noise into an SIC detected value; compensating a channel gain; and performing maximum ration combination (MRC) based on the SIC detected value of which the channel gain is compensated, wherein the step of compensating the channel gain includes an operation of dividing the SIC detected value with the noise inserted by a variance value of the sum of the channel noise and the inserted noise.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method and apparatus for detecting SIC in a multi-

The present invention relates to wireless communication, and more particularly, to a method and apparatus for detecting SIC (succesive interference cancellation) in a MIMO antenna system.

 In a wireless communication system, a fading phenomenon occurs in which a received signal intensity varies with time due to a change in a transmission medium or a path. In order to overcome such a fading phenomenon and to enable high-speed transmission in a next generation wireless communication system, a MIMO (Multiple Input Multiple Output) method of transmitting and receiving a radio signal using a plurality of antennas capable of multiple input and output is used, (For example, forward error correction (FEC)) codes having error correction coding capability. It is very likely that MIMO scheme and error correction code will be used simultaneously in various wireless communication systems in the future.

The error correcting code using repetitive decoding performs calculation by repeatedly using the soft decision input and output in the decoder of the receiving terminal and derives the performance close to the limit of Shannon when the correct soft decision input value is provided can do. Therefore, when the FEC scheme using repetitive decoding such as turbo code and the MIMO scheme using multiple antennas to perform multiple input / output are used at the same time, in the decoding process performed after detection of the MIMO signal, Value is required. Since the reliability of the soft decision input value greatly affects the decoding performance, a method capable of efficiently detecting the soft decision input value is required. In order to solve this problem, a maximum likelihood detection (MLD) method has been proposed. However, since the computational complexity increases exponentially with the number of transmission antennas and modulation order used, have. On the other hand, there is ZFD (zero forcing detection) method with a low complexity detection method, but it is pointed out that the performance deterioration due to the noise enhancement occurring in the detection process is the biggest problem. In order to overcome such a problem, a successive interference cancellation (SIC) method has been proposed. However, in this case, the complexity increases by the number of iterations of the error correcting code.

SUMMARY OF THE INVENTION The present invention provides a method and apparatus for detecting SIC in a wireless communication system.

It is another object of the present invention to provide an SIC detection method and apparatus applicable to a MIMO system.

It is another object of the present invention to provide an SIC detection method and apparatus for reducing complexity and error rate.

According to an aspect of the present invention, there is provided a method for detecting a SIC (succesive interference cancellation) in a multiple input multiple output (MIMO) system. The method includes receiving a MIMO transmission signal, detecting a transmission symbol including a channel noise component based on the received MIMO transmission signal, demodulating a transmission symbol including the channel noise component to obtain bit information Performing SIC detection based on the bit information, inserting noise into the SIC detection value, performing channel gain compensation, and performing MRC based on the channel gain compensated SIC detection value, wherein performing the channel gain compensation comprises dividing the SIC detection value into which the noise is inserted by the variance of the sum of the channel noise and the inserted noise.

According to the present invention, the channel gain can be compensated and the bit error rate (BER) can be reduced upon SIC detection.

In addition, the present invention can achieve good performance without being interlocked with an error correction decoder, and can be used in all systems using SIC.

1 shows a SIC detection method according to an example of the present invention.
FIG. 2 is a block diagram illustrating a transmission / reception system to which conventional sequential interference cancellation is applied.
3 is a block diagram illustrating a transmitting / receiving system to which sequential interference cancellation is applied according to an embodiment of the present invention.
FIG. 4 shows a simulation result of a bit error rate (BER) performance of a receiver according to the present invention.

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference symbols as possible even if they are shown in different drawings. In the following description of the embodiments of the present invention, a detailed description of known configurations or functions will be omitted if it is determined that the gist of the present specification may be obscured.

Furthermore, in describing the components of the specification, when an element is described as being "connected", "coupled" or "connected" to another component, the component may be directly connected to or connected to the other component But it is to be understood that another component may be "connected "," coupled ", or "connected" between each component.

1 shows a SIC detection method according to an example of the present invention.

Referring to FIG. 1, a receiver according to the present invention receives a MIMO transmission signal (S100). The received MIMO signal may be expressed as follows.

Referring to Equation (1), y denotes a received symbol, H denotes a channel gain matrix, s denotes a transmitted symbol, and n denotes channel noise. N _T is the number of transmit antennas, and N _R is the number of receive antennas. H can be a matrix of N _R x N _T. h _mn (m = 1 to N _R , n = 1 to N _T ) denotes a matrix element of H, m denotes a reception antenna index, and n denotes a transmission antenna index.

Referring again to FIG. 1, the receiver detects a transmission symbol including a channel noise component based on the received symbol (S110). This can be performed by the following equation.

Referring to Equation 2,

A transmission symbol including a channel noise component,

Is a transmission symbol detection matrix including a channel noise component.

Is equal to the inverse of the channel gain matrix H.

Referring again to FIG. 1, the receiver demodulates a transmission symbol including the detected channel noise component (S120). In other words, the receiver determines that the transmission symbols including the channel noise component

And outputs the bit information

.

The receiver performs SIC detection based on the bit information (S130). E.g,

Included in

Gt; SIC < / RTI >

Referring to Equation (3), r _i (i.e.,

)

SIC < / RTI > In the existing method,

MRC (Maximum Ratio Combination) is applied as shown in Equation (4) below, and the final signal is detected based on this.

Referring to Equation 4,

(n = 1 to N _R ) represents the complex conjugate value of the corresponding h _1n . When Equation (4) is applied to the SIC detection value r _i as described above, the existing demodulated bit information In the process of SIC detection

The channel gain of the channel is lost, and the accuracy is lowered. Therefore, a new SIC detection is required to compensate the channel gain.

Referring again to FIG. 1, in the present invention, unlike the conventional method of applying Equation (4), noise is inserted into the SIC detected value and the channel gain is compensated (S140). This is as follows.

Referring to Equation 5,

(In other words,

) Represents a value obtained by performing noise injection to the SIC detection value r _i , that is, a noise insertion SIC detection value. The noise insertion is performed by the demodulated bit information

Is assumed to have a noise component. In the symbol demodulation,

In order to solve the problem of disappearing the channel gain. In this case, it is possible to obtain the noise dispersion to compensate the channel gain. The noise variance for compensating the channel gain can be obtained as follows.

Referring to Equation 6,

(In other words,

) Denotes a noise variance value, and VAR denotes a variance. The noise variance value may be a variance value of the sum of the channel noise and the inserted noise. The receiver according to the present invention compensates the SIC detected value obtained by Equation (5) based on the noise variance value calculated in Equation (6) according to the following Equation (7).

Referring to Equation (7)

The SIC detection value with the channel gain compensated,

The SIC detection value inserted in the noise,

Represents the noise variance value.

The receiver performs MRC (Maximum Ratio Combining) based on the SIC detection value with the channel gain compensated (S150). This can be performed by the following equation (8).

Referring to Equation 8,

Represents a value obtained by performing MRC on the channel gain-compensated SIC detection value with respect to S ₁ of the transmitted modulation symbols. Because this value is compensated for the channel gain, the receiver can achieve better performance.

FIG. 2 is a block diagram illustrating a transmission / reception system to which conventional sequential interference cancellation is applied.

Referring to FIG. 2, in the transmitter, the error correction encoder 200 generates a binary bit by adding a parity bit (information) to a binary information bit for correcting an error occurring in a channel, and outputs the binary bit to an M-ary modulator 201). The M-ary modulator 201 maps M bits into one symbol according to a control signal in an upper layer (201). The MIMO transmitter 202 simultaneously transmits the mapped symbols through the multiple antennas to the receiver. The transmitted signal is faded in the channel and channel noise is added.

The receiving end receives the signal to which the fading is applied and the channel noise is added. Specifically, the MIMO receiver 203 of the receiving end detects a signal in which the fading is applied and the channel noise is added as a symbol. The symbol includes a transmission symbol including the channel noise component. The M-ary demodulator 204 demodulates the detected symbols to obtain bit information. The SIC detector 205 performs SIC detection with the bit information detected through the M-ary demodulator 204 and the signal received from the MIMO receiver 203. Thereafter, the MRC unit 207 performs an MRC with the SIC detected signal to detect a symbol, and demodulates it by an M-ary demodulator 208 to detect a bit. The iterative decoder 209 then performs iterative decoding with the SIC detected signal to extract the original information bits.

3 is a block diagram illustrating a transmitting / receiving system to which sequential interference cancellation is applied according to an embodiment of the present invention.

Referring to FIG. 3, a receiving end according to the present invention can directly use a transmitting end (or a transmitting system) to which an existing SIC is applied. That is, the receiving end according to the present invention can receive signals transmitted from the existing transmitting end. The operation of the error correction encoder 300, the M-ary modulator 301, the MIMO transmitter 302, the MIMO receiver 303, the M-ary demodulator 304 and the SIC detector 305 is the same as that of each device The detailed description thereof will be omitted. The signal detected by the SIC detector 305 is transmitted to the channel information inserter 306. The channel information inserter 306 inserts noise into the SIC detection signal (value) as shown in Equation (5), obtains the noise variance value as shown in Equation (6), and outputs the noise inserted SIC detection signal Based on the dispersion value, Equation (7) is applied to obtain the SIC detection signal (value) in which the channel gain is compensated. That is, the channel information inserter 306 compensates channel information that is lost in the conventional method. The MRC unit 307 detects the symbol by performing the MRC with the channel gain-compensated SIC detection signal (value), and demodulates it by the M-ary demodulator 208 to detect the bit. The iterative decoder 209 then performs iterative decoding with the SIC detected signal to extract more accurate original information bits.

FIG. 4 shows a simulation result of the bit error rate (BER) performance according to the system illustrated in FIG. 2 and FIG. The turbo code used in the simulation is a duo-binary turbo code defined as an error correcting code of 'IEEE WiMaX'. The coding rate is 1/3, the frame size is 396 bits, the maximum number of iterations is 8. In addition, all the detection methods at the time of experiment were processed at the front of the decoder without repetition with the iterative decoding of the error correction decoder.

Referring to FIG. 4, Eb / No (energy per bit to noise spectral density ratio) is shown and the vertical axis shows BER. 'Novel ZF-SIC' is a case where the conventional ZF-SIC is combined with the conventional ZF and SIC detection method when 'ZF' is a zero forcing method, 'MLD' indicates the case of the maximum likelihood detection method. As can be seen from FIG. 4, the 'Novel ZF-SIC' method according to the present invention shows a lower bit error rate under the same condition as the conventional 'Conventional ZF-SIC' method. That is, the 'Novel ZF-SIC' method according to the present invention shows better performance than the conventional 'Conventional ZF-SIC' method. In addition, the present invention can achieve good performance without being interlocked with an error correction decoder, and is advantageous in that it can be used in all systems using SIC.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas falling within the scope of the same shall be construed as falling within the scope of the present invention.

Claims (1)

As a method for detecting a SIC (succesive interference cancellation) in a multiple input multiple output (MIMO) system,
Receiving a MIMO transmission signal;
Detecting a transmission symbol including a channel noise component based on the received MIMO transmission signal;
Demodulating a transmission symbol including the channel noise component to obtain bit information;
Performing SIC detection based on the bit information;
Inserting noise into the SIC detection value and performing channel gain compensation; And
And performing a maximum ranging combination (MRC) based on the channel gain-compensated SIC detection value,
Wherein performing the channel gain compensation comprises dividing the SIC detection value inserted with the noise by the variance value of the sum of the channel noise and the inserted noise.

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