KR101229718B1 - Apparatus and method for interference cancellation using mu－mimo schme in single carrier frequency division multiple access system - Google Patents

Abstract

Disclosed are a method and apparatus for eliminating interference between multiple users according to a multi-user multiple input multiple output (MU-MIMO) scheme in a mobile communication system. In this method and apparatus, a reception data former forms channel estimation values and reception data for each terminal from reception signals transmitted from a plurality of terminals, and the selective output device firstly receives relatively low reliability of the received data for each terminal. And the second received data having higher reliability than the first received data, and when only the received data of some terminals of the plurality of terminals is the second received data, the interference signal generator may generate the channel estimate value and the second received data. The interference signal is generated from the second received data, and the SIMO receiver removes the interference signal from the first received data and outputs the interference signal to a higher layer. The present invention can minimize the mutual interference between the received data.

SC-FDMA, MU-MIMO, Interference Cancellation

Description

FIELD OF METHOD AND APPARATUS FOR METHOD OF METHOD USING MV-MIGMO IN SC-FDMA A SYSTEM TECHNICAL FIELD

The present invention relates to a single carrier frequency division multiple access (SC-FDMA) based system, and more particularly, to a method and apparatus for removing interference by applying a subtractive interference cancellation scheme to a multi-user multiple input multiple output (MU-MIMO) scheme. It is about.

Due to various multimedia service requirements in a wireless environment, data transmission capacity and speed are increasing. The method to efficiently use the limited frequency has emerged as a problem to be solved, but unlike the wired channel environment, the wireless channel environment has reliability due to radio wave attenuation, shadowing, time-varying noise, multipath interference, and multi-user interference. Is low.

Multiple Input Multiple Output (MIMO) antenna apparatus includes a plurality of antennas in a transceiver, and enables high-speed data transmission in a limited frequency environment by transmitting and receiving independent information from each transmit / receive antenna. In the MIMO antenna apparatus, there are two methods of removing interference signals of other antennas included in a received signal. The first method is a one-shot multiple-antenna detection method that removes an interference signal by calculating a matrix inverse matrix from the correlation of channels received by several antennas. The second method detects a signal received from one transmitting antenna, reconstructs a signal received from the antenna using the detected signal, and removes the interference signal of the other antenna from the received signal. (subtractive interference cancellation method).

In the non-subtractive interference cancellation scheme, the rank or orthogonal factor of the channel matrix becomes an important factor. That is, in an environment having good orthogonality of the channel matrix, the received signal shows good performance due to low mutual interference component, but in an environment that does not guarantee orthogonality, the mutual interference component remains large and degrades the performance of the MIMO antenna device. . Therefore, in the non-subtractive interference cancellation method, scheduling is performed by estimating mutually orthogonal components of multiple antenna channels.

The subtractive interference cancellation method has been widely studied in the code division multiple access (CDMA) system, and it improves the capacity and performance of the system by reducing the multiple access interference by analyzing and applying signals from multiple terminals similarly to the multiple transmit antenna signals. You can. However, as the terminals are multiplexed, the actual system implementation is not widely used. Recent 3GPP (3 ^rd Generation Partnership Project), which comprises standardized in LTE (Long Term Evolution) system, the downlink OFDMA (Orthogonal Frequency Division Multiple Access) a non-CDMA transmitting and receiving method suitable for a wide frequency scheme and uplink SC-FDMA system Use In addition, in order to maximize frequency efficiency, a SIMO (Single Input Multiple Output) method and a MIMO method may be applied to the uplink and the downlink. In particular, in the uplink, frequency efficiency may be improved by applying a multi-user (MU) MIMO scheme.

FIG. 1 is a diagram illustrating a performance comparison between a case in which two terminals are randomly selected in the uplink using the MU-MIMO scheme and the SIMO scheme. Here, it is assumed that a quadrature phase shift keying (QPSK) coding rate is 0.67, and a 16QAM (quadrature amplitude modulation) coding rate is 0.76. The number of used subcarriers is 432. As shown in FIG. 1, when the signal received from the SIMO terminal is scheduled in the MU-MIMO scheme, additional power of about 4 dB (QPSK) and 7 dB (16 QAM) is required.

2 illustrates an example of resource allocation scheduling of a user equipment (UE) in the uplink. UE1, UE4-6 are allocated resources by SIMO method, and UE2 and 3 are allocated resources by MU-MIMO method. UE1, UE4-6 may be distinguished by subcarrier demapping in the frequency domain by using user resource allocation information. However, UE2 and UE3 scheduled in the MU-MIMO scheme cannot be distinguished by using the same frequency band even through subcarrier demapping, so they are distinguished through an equalizer. A scheduler may determine a correlation between user channels and allocate a pair of less related users in a pair, but this is difficult to implement in an actual system. In particular, in a broadband communication system, since frequency selective fading is experienced, it is impossible to find a case where there is no mutual interference between user channels. In addition, LTE systems, which aim to accommodate more than 200 users in one cell, have a very large user combination for obtaining correlations among users in a cell. Therefore, in a real MU-MIMO system, random scheduling is inevitable. For this reason, the MU-MIMO scheme using random scheduling has a problem in that a performance degradation of about 4-7 dB occurs compared to the SIMO scheme.

The present invention provides an interference cancellation method and apparatus for preventing performance degradation of a multi user-multiple input multiple output (MU-MIMO) scheme in a single carrier frequency division multiple access (SC-FDMA) system.

An interference cancellation apparatus of an SC-FDMA system of the present invention includes: a reception data generator configured to form channel estimation values and reception data for each terminal from reception signals transmitted from a plurality of terminals; The received data for each terminal is classified into first received data having a relatively low reliability and second received data having a higher reliability than the first received data, and only received data of some terminals of the plurality of terminals includes the second received data. A selection outputter configured to output the second received data to a higher layer in the case of: An interference signal generator for generating an interference signal from the second received data with reference to the channel estimate value and the second received data; And a SIMO receiver which removes the interference signal from the first received data and outputs the interference signal to a higher layer.

In addition, the interference cancellation method of the SC-FDMA (Single Carrier Frequency Division Multiple Access) system of the present invention comprises the steps of: the receiving data former to form a channel estimation value and received data for each terminal from the received signals transmitted from a plurality of terminals; Selecting, by the selection output unit, the received data for each terminal into first received data having relatively low reliability and second received data having higher reliability than the first received data; Outputting the second received data to a higher level when any one of the received data for each terminal is second received data; Generating, by the interference signal generator, an interference signal from the second received data with reference to the channel estimate and the second received data; And removing, by the SIMO receiver, the interference signal from the first received data and outputting the interference signal to a higher layer.

The present invention can reduce the complexity of the system in the SC-FDMA-based system using MU-MIMO and can improve the reception performance by minimizing mutual interference.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Multiple input multiple output (MIMO) antenna apparatus is capable of high-speed data transmission in a limited frequency environment by transmitting and receiving independent information between a plurality of transmit and receive antennas. As shown in FIG. 3, a 2 × 2 multiuser multiple input multiple output (MU-MIMO) system including two transmit / receive antennas has a channel response that means channel estimates of multiple terminals as shown in Equation (1).

In Equation 1, H _n is a channel response of n terminal, and h _xy is a channel response for y transmit antenna and x receive antenna.

4 is a block diagram illustrating an MU-MIMO interference cancellation apparatus 100 of a single carrier frequency division multiple access (SC-FDMA) based system according to an exemplary embodiment of the present invention. The reception data generator 110 forms channel estimation values for each terminal and reception data for each terminal from the reception signals transmitted from a plurality of terminals. More specifically, the CP (cyclic prefix) remover 111 of the reception data generator 110 removes the CP included in the received signal to eliminate interference by the multipath channel. The fast fourier transforming unit 112 converts a signal in the time domain into a signal in the frequency domain to form a transform signal R (k) expressed by Equation 2.

In Equation 2, N is an FFT size determined according to a system bandwidth, and particularly, has a value of 1024 in a 10Mhz bandwidth.

The subcarrier demapping unit 113 extracts only the signal of the subcarrier transmitted by the UE from the converted signal R (k) to form a demapping signal Y (k) expressed by Equation 3 below.

In Equation 3, N _u represents the total number of subcarriers allocated to the transmitter, and N_Offset represents the start position of the subcarrier.

The channel estimator 114 receives the demapping signal and estimates a channel value corresponding to each terminal. The MU-MIMO equalizer 115 receives a channel response H (k) representing a channel estimate value and a demapping signal Y (k), and performs an equalization process for forming a channel compensation signal X (k) with a wireless channel compensated. (equalizing). The channel compensation signal is formed for each terminal as shown in FIG.

The channel compensation signal in the MU-MIMO method using a minimum mean squared error (MMSE) method, which is a kind of non-subtractive interference cancellation method having a low complexity, is expressed by Equation 4.

는 백색잡음의 전력, Y(k)는 디맵핑신호의 신호 벡터이다. 수학식 4를 참조하면, 두 단말의 신호들이 겪는 채널 특성 사이에 연관되는 값에 의하여 간섭 성분이 채널 보상 신호 X(k)에 남게 되며, 간섭 성분의 크기에 따라 수신 성능이 좌우된다.In Equation 4,

Is the power of white noise, and Y (k) is the signal vector of the demapping signal. Referring to Equation 4, an interference component remains in the channel compensation signal X (k) by a value associated between channel characteristics experienced by signals of two terminals, and reception performance depends on the magnitude of the interference component.

An inverse discrete fourier transforming unit (IDFT unit) 116 converts the channel compensation signal X (k) in the frequency domain into a time domain channel compensation signal. The demodulator 117 demodulates a compensation signal of a time domain channel to form a demodulation signal. Decoder 118 decodes the demodulated signal to form received data for each terminal.

In the present exemplary embodiment, the reception data generator 110 includes two IDFT units 116, demodulators 117, and decoders 118 according to the number of terminals, but the present invention is not limited thereto. There may be a plurality of IDFT units 116, demodulators 117, and decoders 118 depending on the number of.

The selection outputter 120 performs a cyclic redundancy code (CRC) test included in the reception data of each terminal to include the interference data in the reception data of each terminal, and thus does not include the first reception data and the interference component having low reliability. Is classified as high second received data. In addition, the selection outputter 120 outputs a channel estimation value selection signal for extracting the interference signal. If the CRC is not accurate (CRC NOK), it is classified as received data (first received data) that includes an interference signal. If the CRC is correct (CRC OK), received data (second received data that does not include an interference signal) Classify as) The second received data determined that the CRC information is correct (CRC OK) does not require any further signal processing, and only the channel estimate selection signal of the second received data for extracting the interference signal is used in the interference extractor 130. . That is, since the interference component of the other terminal does not need to be removed from the received data of the corresponding terminal, the present invention has an advantage of greatly reducing the complexity compared to the subtractive interference cancellation scheme in which the interference component must be removed from all the terminal signals. In order to further increase the complexity reduction effect, the selection output unit 120 transmits the received data to a higher layer without the interference signal elimination procedure when it is determined that the reliability of the interference signal to be subtracted is insufficient or that all of the signals have already been completely processed. Report and terminate the receiving procedure. The selection output unit 120 determines whether to remove the interference signal using the CRC because information on the presence or absence of the CRC error can maximize the reliability of the interference signal. When all CRCs belonging to the received data of a specific terminal are determined to be correct (CRC OK), the reliability of the reproduction signal of the corresponding user data may be maximum. In this way, the complexity of the interference signal cancellation process can be reduced by solving the reliability determination problem using the CRC. In the present embodiment, the subtraction trust is determined using the CRC information. However, in addition to the CRC information, reliable information such as a signal to interference and noise ratio (SINR) may be used.

Referring to FIG. 5, the interference signal generator 130 generates a coding block 131, a CRC generation 132, a turbo encoding 133, and a data modulation 134 on the second received data. ) And a discrete fourier transform (DFT) process 135, a channel estimate value of the first and second received data is received from the channel estimator 114, and a channel estimate value selection signal is received from the selection outputter 120. The DFT generates the interference signal I (k) from the second received data.

The interference canceling unit 141 of the SIMO receiver 140 removes the interference signal I (k) from the demapping signal Y (k) received from the MU-MIMO receiver 110, Outputs the interference cancellation signal Y` (k) expressed as follows.

The SIMO equalizer 142 forms an output signal of the equalizer 142 represented by Equation 6 using the interference cancellation signal Y ′ (k) and the channel estimate value input from the channel estimator 114.

는 백색잡음의 전력, Y`(k)는 간섭 제거 신호의 신호 벡터이다.In equation (6)

Is the power of white noise, and Y` (k) is the signal vector of the interference cancellation signal.

The receiver IDFT unit 143 converts the output signal of the SIMO equalizer 14 into a signal in the time domain. The receiver demodulator 144 demodulates the time domain signal. The receiver decoder 145 decodes the coded demodulated signal to form a decoded signal. The CRC checker 146 performs the CRC check included in the decoded signal, outputs the first received data that has been removed from interference, reports it to a higher layer, and ends all receiving procedures.

As described above, the interference cancellation apparatus 100 according to the embodiment of the present invention can reduce the complexity of the subtraction receiver of the conventional CDMA that performs interference cancellation in the time domain by removing the interference component in the frequency domain.

6 shows a performance gain of 2dB to 3dB in QPSK and 16QAM when the proposed method is used as a result of simulation under the conditions using QPSK Coding Rate = 0.67 and 16QAM Coding Rate = 0.76 and 432 subcarriers.

As another embodiment of the present invention, a system may be configured to enable a spatial-division multiple access (SDMA) scheme in an SC-FDMA system. SDMA uses multiple receive antennas to form multiple beams in one sector. If four reception antennas are used and two terminals are scheduled at the same time, the channel response may be extended as shown in Equation (7).

When the two terminals are in the overlapping area of the beam, the present invention can be extended to four antennas, and even if one terminal is assigned to each beam, it can be regarded as a special case of 2x4 MU-MIMO. It is expressed as

However, h ₁₂ , h ₂₂ , h ₃₁ , and h ₄₁ represented by "0" in the above equations have some values in actual situations, causing interference between multiple terminals. Even in such a case, performance gain can be obtained by using the interference cancellation method of the present invention.

Those skilled in the art to which the present invention pertains will understand that the present invention can be implemented in other specific forms without setting the technical spirit or essential features. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is shown by the following claims rather than the detailed description, and all settings or modifications derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present invention. do.

FIG. 1 is a diagram illustrating a performance comparison when a MU-MIMO method is used by randomly selecting a SIMO method and two terminals in an uplink of an SC-FDMA system.

2 is an exemplary view showing "resource allocation" scheduling of the terminal.

3 is a block diagram of an SC-FDMA system in which two UEs are scheduled according to an embodiment of the present invention.

4 is a block diagram showing a device for removing interference in an SC-FDMA system according to an embodiment of the present invention.

5 is a block diagram showing a configuration of an interference signal generator according to an embodiment of the present invention.

6 is a view showing the performance comparison between the interference cancellation method and the conventional interference removal method according to an embodiment of the present invention.

** Explanation of symbols on the main parts of the drawing **

CINR: Carrier to Interference and Noise Ratio

BLER: Block Error Rate

Claims (9)

An interference cancellation apparatus using a single carrier frequency division multiple access (SC-FDMA) scheme, A reception data generator configured to form channel estimation values and reception data for each terminal from reception signals transmitted from a plurality of terminals; The received data for each terminal is classified into first received data having a relatively low reliability and second received data having a higher reliability than the first received data, and only received data of some terminals of the plurality of terminals includes the second received data. A selection outputter configured to output the second received data to a higher layer in the case of: An interference signal generator for generating an interference signal from the second received data with reference to the channel estimate value and the second received data; And And a SIMO receiver for removing the interference signal from the first received data and outputting the interference signal to a higher layer. In accordance with paragraph 1, The selective output unit, And all the received data for each terminal is classified as the first received data or the second received data, and further operates to output all of the received data for each terminal to an upper layer. In accordance with paragraph 2, The reception data former is A CP remover configured to remove a cyclic prefix (CP) included in the received signal to eliminate interference by a multipath channel; A fast fourier transforming unit for converting the CP-received received signal into a signal in a frequency domain to form a transformed signal; A subcarrier demapping unit (subcarrier demapping unit) for extracting only a subcarrier signal transmitted by the terminal from the converted signal to form a demapping signal; A channel estimator receiving the demapping signal and estimating a channel value according to each terminal; A MU-MIMO equalizer for receiving the channel estimation value and the demapping signal for each terminal and forming a channel compensation signal with a wireless channel compensated; An IDFT unit for converting the channel compensation signal into a time domain channel compensation signal; A demodulator for recovering the time domain channel compensation signal to form a demodulated signal; And And a decoder configured to decode the demodulated signal to form received data for each terminal. In accordance with paragraph 3, The interfering signal generator, Receiving the second received data, coding block generation, CRC (Cyclic Redundancy Code) generation, turbo encoding, data modulation, discrete fourier transform (DFT) process and channel estimation value for each terminal, the And an interference canceling device for generating an interference signal by receiving a channel estimate selection signal. In accordance with paragraph 4, The SIMO receiver is An interference canceling unit configured to remove the interference signal from the de-mapping signal and output an interference cancellation signal; A SIMO equalizer for forming a channel compensation signal in which a wireless channel is compensated from the interference cancellation signal and the channel estimate value; A receiver DFT unit for converting the channel compensation signal into a time domain channel compensation signal; A receiver demodulator for recovering the time domain channel compensation signal to form a demodulated signal; A receiver decoder for decoding a demodulated signal coded from the demodulated signal to form a decoded signal; And And a CRC checker configured to perform a CRC check included in the decoded signal and output first interference-received data. A method for canceling interference in a SC-FDMA (Single Carrier Frequency Division Multiple Access) system, a) a step of forming, by the reception data former, channel estimation values and reception data for each terminal from reception signals transmitted from a plurality of terminals; b) a selective output unit classifying the received data for each terminal into first received data having a relatively low reliability and second received data having a higher reliability than the first received data; c) outputting the second received data to a higher level when any one of the received data for each terminal is the second received data; d) generating, by the interference signal generator, the interference signal from the second received data with reference to the channel estimate and the second received data; And e) a SIMO receiver removing the interference signal from the first received data and outputting the interference signal to a higher layer. The method of claim 6, C), And outputting all received data for each terminal to a higher layer if all received data for each terminal is classified as the first received data or the second received data. The method of claim 7, wherein Step a) is Performing a cyclic prefix (CP) removal included in the CP removing unit to eliminate interference by the multipath channel in the received signal; A fast fourier transforming unit (FFT) converting the CP-received received signal into a signal in a frequency domain to form a transformed signal; A subcarrier demapping unit extracting only a signal of a subcarrier transmitted by the terminal from the converted signal to form a demapping signal; Receiving, by a channel estimator, the demapping signal to form a channel estimate for each terminal; Receiving, by a MU-MIMO equalizer, the channel estimation value and the demapping signal for each terminal, and forming a channel compensation signal compensated for a wireless channel; An IDFT unit converting the channel compensation signal into a time domain channel compensation signal; Demodulating the time domain channel compensation signal to form a demodulation signal; And And decoding a demodulated signal coded from the demodulated signal to form received data for each terminal. 9. The method of claim 8, Step e), Outputting an interference cancellation signal by removing the interference signal from the demapping signal by an interference cancellation unit; Forming, by a SIMO equalizer, a channel compensation signal in which a wireless channel is compensated with reference to the interference cancellation signal and the channel estimate value; A receiver DFT unit converting the channel compensation signal into a time domain channel compensation signal; A receiver demodulation unit recovering the time domain channel compensation signal to form a demodulation signal; A receiver decoder decoding the demodulated signal to form a decoded signal; And And a CRC checker performing a CRC check included in the decoded signal and outputting first interference-received received data to a higher layer.

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