KR101219985B1 - Scheduling methods and apparatus for using interference cancelling - Google Patents

Abstract

PURPOSE: A scheduling method using an interference elimination method and an apparatus thereof are provided to improve the reception performance of a signal from other users by increasing the effect of eliminating a signal of a specific user by reliably transmitting the signal. CONSTITUTION: An SIR(signal-to-interference ratio) setup unit(120) sets a target SIR by considering an MCS(modulation and coding scheme) corresponding to users. A user pairing unit(130) sets two users for using one frequency band in one time slot by considering the target SIR. A control unit(140) set a schedule of users in order to improve the reliability of a reception signal of the users. [Reference numerals] (110) MCS setup unit; (120) SIR setup unit; (130) User pairing unit; (140) Control unit

Description

SCHEDULING METHODS AND APPARATUS FOR USING INTERFERENCE CANCELLING

The present invention relates to long term evolution (LTE), and more particularly, to a scheduling method and apparatus using a subtractive interference cancellation scheme.

"This study was carried out as a result of the study of the original technology development project of the next generation communication network of the Korea Communications Commission" (KCA-2011-10913-04002)

The market for wireless communication is growing rapidly and the demand for various multimedia services in a wireless environment is increasing the capacity and speed of data transmission. Therefore, the method that can effectively use the limited frequency has emerged as the most urgent problem to solve, but unlike the channel environment of wireless communication, the channel environment of radio communication has attenuation, shadowing, time-varying noise, multipath interference, Low reliability due to multi-user interference or the like. Therefore, various techniques for efficiently using limited frequency resources have been studied to overcome the low reliability of wireless communication.

A multiple input multiple output (MIMO) antenna system is a system including a plurality of antennas in a transmission and reception apparatus, and enables high-speed data transmission in a limited frequency environment by transmitting independent information using each transmission antenna. There are two main ways to detect MIMO transmission information. First, the one-shot multiple-antenna detection method, which is a non-subtractive interference cancellation method that detects multiple signals by performing matrix inverse matrix calculation from the correlation of reception channels from several antennas. The second method is to first remove the interference signal for another antenna by reconstructing and subtracting the received signal from the antenna using the result of the detected signal after detecting the reception signal for one reception antenna. There is a subtractive interference cancellation method.

Finding a scheduling user pair with orthogonality, which is an essential element of a general interference cancellation scheme, greatly increases the complexity of the scheduler. That is, there is a disadvantage in that all orthogonalities between scheduling candidate groups must be obtained in every scheduling period. For example, if there are N candidate users to be considered for scheduling, it is necessary to find an appropriate scheduling user pair based on the results obtained through the orthogonality test of N * (N-1) / 2. Since there are generally hundreds of users in an LTE base station, the complexity of implementing orthogonality tests is an important factor that impedes the practical use of the MU-MIMO scheduling scheme.

Actual wireless communication systems generally perform random scheduling on orthogonality without obtaining orthogonality. FIG. 1 shows the performance of a non-subtractive interference cancellation apparatus in the case of using the SIMO scheduling scheme and in the case of using the MU-MIMO scheduling scheme by randomly selecting two users. In FIG. 1, it is assumed that 16QAM (quadrature amplitude modulation) coding rate is 0.5 and 48 used uplink resource blocks. As shown in FIG. 1, when the SIMO scheduling user is scheduled using the MU-MIMO scheduling method, an additional power of about 6 dB is required. This indicates that when the user is randomly selected, the correlation between the channel values of the two users remains in the signal after passing through the equalizer, thereby degrading performance. The performance degradation due to the exclusion of orthogonality estimation has a problem of greatly reducing the advantages of the originally intended MU-MIMO scheduling scheme.

Korean Patent Publication No. 10-2010-0013927 (published Feb. 10, 2010)

The present invention provides a scheduling method and apparatus using a subtractive interference cancellation scheme.

In the scheduling apparatus using the interference cancellation method of the present invention, an MCS setting unit configured to set a modulation and coding scheme (MCS) for each user in consideration of transmission power and a buffer of at least two users transmitting a signal. ; An SIR setting unit configured to set a target signal-to-interference ratio in consideration of the user-specific MCS; A user pairing unit for setting two users forming a user pair for using the same frequency band among the at least two users transmitting the signal in the same time period in consideration of the target signal-to-interference ratio; And a controller configured to perform scheduling to improve the reliability of a received signal of any one user forming the user pair.

In addition, the scheduling method using the interference cancellation method of the present invention, a) selecting at least two users forming a user pair (user pair) for using the same frequency band in the same time zone of the at least two users transmitting the signal; And b) performing scheduling to improve received signal reliability of any one user of the user pair.

According to the present invention, a signal of a specific user is transmitted and removed with high reliability, thereby increasing the reception performance of another user's signal, and also increasing the throughput of the system as a whole. Bring.

1 is an exemplary diagram showing link performance of SIMO and random pairing MU-MIMO.
2 is an exemplary view showing an MU-MIMO environment in which two users are scheduled according to an embodiment of the present invention.
3 is a block diagram showing a structure of a SIMO receiver in SC-FDMA according to an embodiment of the present invention.
4 is a block diagram illustrating a structure of a MU-MIMO receiver in SC-FDMA according to an embodiment of the present invention.
5 is an exemplary view showing a subcarrier mapping and an SC-FDMA subframe structure according to an embodiment of the present invention.
6 is a block diagram showing a receiver structure according to the application of a subtractive interference cancellation scheme for MU-MIMO according to an embodiment of the present invention.
7 is a block diagram showing a structure of an interference signal regenerator according to an embodiment of the present invention.
8 is an exemplary diagram illustrating scheduling in 3GPP LTE uplink according to an embodiment of the present invention.
9 is a block diagram showing a configuration of an uplink scheduling apparatus according to an embodiment of the present invention.
10 is an exemplary diagram showing link performance when random scheduling and 2 dB boosting of Method 1 according to an embodiment of the present invention are applied.
FIG. 11 is an exemplary diagram showing link performance when random scheduling and 2 dB boosting of method 1 are applied. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions will not be described in detail if they obscure the subject matter of the present invention.

The 3GPP LTE (3rd generation partnership project long term evolution) system transmits / receives a downlink orthogonal frequency division multiple acces (OFDMA) scheme and an uplink single carrier frequency division (SC-FDMA) scheme instead of code division multiple access (CDMA) to fit a wideband frequency. multiple access). In addition, in order to maximize frequency efficiency, MIMO (multiple input multiple output) scheme is applied to the uplink and downlink. In particular, uplink uses MU-MIMO (MU-MIMO) to improve frequency efficiency. As shown in FIG. 2, the MU-MIMO assumes that the transmit antennas are located at different terminals, and has a channel response that means a channel estimate value as shown in Equation (1).

In Equation 1, H _n represents a channel response of n terminal, and h _xy represents a channel response for y transmit antenna and x receive antenna. That is, H ₁ represents the channel response of the first terminal x ₁ , and H ₂ represents the channel response of the second terminal x2. And, h ₁₁ is a first channel in response to a first receiving antenna (y ₁₎ of transmission antennas (x _1), h ₁₂ is for a second receiving antenna (y ₂₎ of the first transmission antenna (x ₁₎ Is the channel response, h ₂₁ is the channel response to the first receive antenna y ₁ of the second transmit antenna x ₂ , and h ₂₂ is the second receive antenna y ₂ of the second user x ₂ . Represents the channel response for

FIG. 3 is a block diagram illustrating a configuration of a single input multiple output (SIMO) receiving apparatus in 3GPP LTE uplink according to an embodiment of the present invention, and FIG. 4 is a MU-MIMO in 3GPP LTE uplink according to an embodiment of the present invention. A block diagram showing the configuration of a receiving device. Since the LTE uplink uses the SC-FDMA scheme, the baseband received signal passes through a cyclic prefix remover (CP) and a fast Fourier transform unit (FFT) in a SIMO or MU-MIMO receiver. The CP remover removes the CP included in the received signal to eliminate interference by the multipath channel. The FFT unit converts a signal in the time domain into a signal in the frequency domain to form a converted signal R (k) expressed as in 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 extracts only the signal of the subcarrier transmitted from the UE from the converted signal R (k) to form a demapping signal Y (k) expressed by Equation 3 below. As shown in FIG. 5, the receiving end shows which subcarriers should be extracted. The receiving device can obtain only a specific user's signal using the values of N_Offset and N _u .

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 receives the demapping signal and estimates a channel value corresponding to each terminal. The SIMO or MU-MIMO equalizer equalizes to receive the channel response H (k) and demapping signal Y (k), which mean channel estimates, and to form the channel compensation signal X (k) with the wireless channel compensated. Do this. The channel compensation signal is formed for each terminal as shown in FIGS. 3 and 4. Using a minimum mean squared error (MMSE) method, which is a type of non-subtractive interference cancellation method having a low complexity, the channel compensation signal in the SIMO or MU-MIMO scheduling method may be represented as shown in Equation 4 below.

는 SIMO 스케쥴링 방식에서의 채널 보상 신호를 나타내고,

는 MU-MIMO 스케쥴링 방식에서의 채널 보상 신호를 나타내고,

은 백색잡음의 전력을 나타내며, Y(k)는 디맵핑 신호의 신호 벡터를 나타낸다. MU-MIMO 등화부의 채널 보상 신호를 보면 두 사용자 신호들이 겪는 채널 특성 사이에 연관되는 값에 의한 간섭이 채널 보상 신호에 남게 되며, 간섭의 크기에 따라서 수신 장치 성능이 좌우된다.In Equation 4,

Represents a channel compensation signal in the SIMO scheduling scheme,

Represents a channel compensation signal in the MU-MIMO scheduling scheme,

Denotes the power of white noise, and Y (k) denotes the signal vector of the demapping signal. In the channel compensation signal of the MU-MIMO equalizer, interference due to a value associated between channel characteristics experienced by two user signals is left in the channel compensation signal, and the performance of a receiving device depends on the magnitude of the interference.

After passing through the SIMO or MU-MIMO equalizer, it passes through the IDFT unit, the demodulator, and the decoding unit.

The IDFT unit (Inverse Discrete Fourier Transforming unit) converts the channel compensation signal X (k) in the frequency domain into a time domain channel compensation signal. A demodulator demodulates a compensation signal of a time domain channel to form a demodulated signal. The decoding unit decodes the demodulated signal to form received data for each terminal. A cyclic redundancy check (CRC) checker checks the CRC of the received data for each terminal. If there is no error in the CRC (CRC OK), it is determined that there is no error in the received data. If there is an error in the CRC (CRC NOK), it is determined that there is an error in the received data.

The MU-MIMO scheduling method receiving apparatus of FIG. 4 includes two IDFT units, demodulators, decoders, and CRC check units according to the number of terminals. However, the present invention is not limited thereto. A plurality of decoding units and CRC check units may exist.

On the other hand, using a subtractive interference cancellation scheme can be configured as shown in FIG. The reception apparatus of the subtractive interference cancellation method generates an interference signal for each user UE1 and UE2 using the received data of each user UE1 and UE2. For example, assuming that only two users exist, generate both interference signals for each of the two users. 7 is a diagram illustrating a procedure of an interference signal generating method according to an embodiment of the present invention. The interference signal generator first performs coding block generation, CRC generation, turbo encoding, data modulation, and discrete fourier transform (DFT) processing on received data of each terminal, and receives SIMO or MU-MIMO. The channel estimation unit (H (k)) of the received data for each terminal is received from the channel estimator of the device to generate an interference signal from the received data for each terminal where the DFT is completed. The interference canceling unit removes interference of other user signals from the stored received signal using the generated interference signals. Therefore, since the interference signal removed by each user is different, the signals after the interference removal are different, and this signal is used as the input of the SIMO equalizer of each user.

Assuming that there are two receiving antennas of the base station and resources are allocated by the uplink scheduler as shown in FIG. 8, UE1 and UE4 to 6 use the SIMO scheduling scheme, and UE2 and UE3 use the same frequency band in the same time zone. Since two users form a scheduling user pair, the MU-MIMO scheduling method is used. Since users are allocated resources using the SIMO scheduling method, subcarriers in the frequency band are separated from each other. However, mutual interference does not exist, but there is mutual interference between users allocated resources using the MU-MIMO scheduling method. As an embodiment, when the CRC check is performed through the MU-MIMO scheduling method, if it is assumed that there is no abnormality in the CRC only in the received data of the UE2, the interference signal generator generates the interference signal using the received data of the UE2. If the channel response H (k), which is a channel estimation value determined by the MU-MIMO channel estimator, is equal to Equation 5, the interference signal generation uses the channel response H ₂ (k) of UE2 and the SIMO equalization signal from which the interference canceled signal is input. In the section, H ₃ (k), which is a channel response of UE3, is used. The interference signal I (k) formed by the interference signal generator indicates a signal of UE2. The interference cancellation unit removes the interference signal I (k) from the demapping signal Y (k) in which all signals of the UE2 and the UE3 are mixed to form the interference cancellation signal Y '(k). Only the signal of UE3 remains in the interference cancellation signal. The interference cancellation signal Y '(k) passes through the SIMO equalizer, the IDFT unit, the demodulator, the decoder, and the CRC checker to obtain the reception data of UE3.

In the SIMO scheduling scheme, a modulation and coding scheme (MCS) and a scheme are considered in consideration of two aspects of power control considering a user equipment (UE) buffer state and a user terminal transmission power (Tx power). The user terminal transmit power is determined for each user, and scheduling for the upcoming transmission section is performed. Meanwhile, the MU-MIMO scheduling method determines the final schedule after setting the MU-MIMO scheduling decision element among several users in addition to the MCS and user terminal transmission power determined for each user in the SIMO scheduling method.

(A) Orthogonality Determination for MIMO Scheduling

In the non-subtractive interference cancellation scheme, the rank or orthogonal factor of the channel matrix becomes an important factor of the MIMO scheduling. In other words, in the state of good orthogonality of the channel matrix, the signal after multi-signal detection has a small amount of mutual interference, and exhibits good performance. However, in the state of poor orthogonality, the signal after multi-signal detection has a large mutual interference component. Remaining to degrade reception performance. Therefore, in the non-subtractive interference cancellation method, a good signal reception result can be obtained by estimating and scheduling mutual orthogonal components of multiple antenna channels. In addition, MU-MIMO scheduling can be used to achieve good reception performance only when signals transmitted simultaneously at the transmitting end arrive at the receiving end with similar receiving strength.

On the other hand, the subtractive interference cancellation method generates an interference signal using a signal after an equalizing process and a decoding process, removes an interference signal generated for input signals of different users, and then receives a SIMO method reception. Since the interference signal elimination criterion is higher than that of the non-subtractive method determined at the channel end, the interference signal estimation reliability is higher. In other words, the subtractive interference cancellation scheme improves reception performance instead of increasing the reception complexity than the non-subtraction interference cancellation scheme. In addition, even in a subtractive interference cancellation scheme, the equalization process is initially performed, so whether orthogonality judgment has a great influence on reception performance.

(B) Scheduling with buffer and power control in mind

In the non-subtracted interference cancellation method, the receiving apparatus receives information about the buffer state and the transmit power strength of the user terminal from the user terminal, and uses the target SIR for each MCS using the non-subtracted interference cancellation transmission method in the scheduler. Determine MCS by considering Interference Ratio. Thereafter, a scheduling user pair is selected using random scheduling among the interference cancellation transmission candidate group of the user.

In the subtractive interference cancellation method, if one user's received signal is highly demodulated and accurately demodulated, the demodulated signal of another user's received signal also increases considerably since such a demodulated signal can be accurately removed from another user's received signal. Can increase the throughput within

9 is a block diagram showing the configuration of an uplink scheduling apparatus according to an embodiment of the present invention.

As shown in FIG. 9, the uplink scheduling apparatus 100 includes an MCS setting unit 110, an SIR setting unit 120, a user pairing unit 130, and a controller 140.

The MCS setting unit 110 sets a modulation and coding scheme (MCS) for each user in consideration of a user terminal buffer state for transmitting a signal and a user terminal transmission power.

The SIR setting unit 120 sets a target signal-to-interference ratio (TIR) in consideration of the user-specific MCS set in consideration of the buffer state and the transmission power in the MCS setting unit 110.

The user pairing unit 130 may be configured to use the same frequency band in the same time period among a plurality of users transmitting signals in consideration of the target signal-to-interference ratio set by the SIR setting unit 120 using the MCS for each user. Set up two users in a user pair).

The control unit 140 performs scheduling so that the reliability of the received signal of any one of the users who form the user pair set by the user pairing unit 130 can be improved. There are two ways to improve the reliability of the received signal of any one of the users constituting the scheduling user pair.

(Method 1)

A method of increasing reception demodulation reliability of a reception signal of a receiver by artificially adjusting a transmission power strength of one of two users constituting a scheduling user pair by a predetermined value. As one embodiment, it may be implemented in the following way.

1. The user-specific MCS is selected in consideration of the performance of the subtractive interference cancellation device in the same reception environment, the transmission power of each user, and the buffer, and the target SIR represents the SIR of the received signal required by the selected user-specific MCS.

2. For the MCS selected in 1, find the user with sufficient transmit power margin among all users. In other words, a user whose transmission power surplus is larger than the threshold Target_SIR_boost is selected. According to an embodiment, Target_SIR_boost representing a transmission power extra threshold may be a target SIR in consideration of transmission power boosting. Change Target SIR of a user who satisfies the condition that Target_SIR_boost ≤ Tx_power_margin_user to a value considering Target_SIR_boost. The modified Target SIR may be represented as shown in Equation 6.

In Equation 6, New_target_SIR represents the changed target SIR of the user whose transmit power surplus is greater than the threshold, and Target SIR represents the target SIR before the change of the user whose transmit power surplus is greater than the threshold, and Target_SIR_boost takes into account transmission power boosting. Target SIR.

3. Find all users except the user selected in 2 and select them as MU-MIMO scheduling user pair.

4. Increase the transmit power strength of any one of the users of the MU-MIMO scheduling user pair selected in step 3.

(Method 2)

A method of increasing reception demodulation reliability of a receiving end by reducing an MCS of one of two users constituting a scheduling user pair than an appropriate MCS and transmitting the same. As an embodiment, it may be implemented as follows.

1. Select MCS for each user considering the performance of subtractive interference cancellation device in the same reception environment, transmission power and buffer of each user, and set Target SIR to SIR of received signal required in selected MCS for each user.

2. Select two suitable users from the candidate user group of 1 as the scheduling user pair.

3. The target SIR of any one of the scheduling user pairs selected in 2 is reduced as in Equation 7.

In Equation 7, New_target_SIR represents a changed target SIR of one of the users constituting the scheduling user pair, the target SIR represents a target SIR before the change of any one of the users constituting the scheduling user pair, and Target_SIR_boost boosts transmission power. Target SIR is considered.

4. Perform scheduling to reset the MCS in consideration of the reduced target SIR.

In the non-subtracted interference cancellation scheme, when a transmission power boosting is applied to any one user as in the method 1, as shown in FIG. 10, the boost user has good performance and the other users have constant performance. Indicates. The graph of FIG. 10 is a result of boosting the transmission power of one user by 2 dB when MU-MIMO is used by randomly selecting two users of FIG. 1.

However, in the subtractive interference cancellation method, one user is transmitted with high reliability and is removed, thereby increasing the reception performance of another user's signal. FIG. 11 is a graph showing the performance when a receiver is replaced with a subtractive receiver under the same condition as in FIG. 10. Unlike the case of using the non-subtracted interference cancellation method, the boosting effect of the transmission power also helps the reception performance of the non-boost user. Therefore, boosting will increase the throughput of the system as a whole.

The above embodiment describes a scheduling method of MU-MIMO for scheduling different users for LTE uplink. Since the standard is evolved to support not only MU-MIMO but also single-user MIMO (SU-MIMO) in the LTE uplink, the above-described embodiments can be applied among various ranks of SU-MIMO.

While the above methods have been described through specific embodiments, the methods may also be implemented as computer readable code on a computer readable recording medium. A computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored. Examples of the computer-readable recording medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, and the like, and may be implemented in the form of a carrier wave (for example, transmission over the Internet) . In addition, the computer-readable recording medium may be distributed over network-connected computer systems so that computer readable codes can be stored and executed in a distributed manner. In addition, functional programs, codes, and code segments for implementing the above embodiments can be easily deduced by programmers of the present invention.

Although the present invention has been described in connection with some embodiments thereof, it should be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention as understood by those skilled in the art. something to do. It is also contemplated that such variations and modifications are within the scope of the claims appended hereto.

100: uplink scheduling apparatus 110: MCS setting unit
120: SIR setting unit 130: user pairing unit
140:

Claims (8)

An uplink scheduling apparatus,
An MCS setting unit configured to set a modulation and coding scheme (MCS) for each user in consideration of transmission power and a buffer of at least two users transmitting a signal;
An SIR setting unit configured to set a target signal-to-interference ratio in consideration of the user-specific MCS;
A user pairing unit for setting two users forming a user pair for using the same frequency band among the at least two users transmitting the signal in the same time period in consideration of the target signal-to-interference ratio; And
And a controller configured to perform scheduling to improve received signal reliability of any one user of the user pair. The method of claim 1,
The control unit,
Uplink scheduling apparatus for performing a scheduling to increase the transmission power strength of any one of the users constituting the user pair a predetermined value. The method of claim 2,
The user pairing unit,
Uplink scheduling apparatus for selecting a user pair having a transmission power margin equal to or greater than a threshold value among at least two users transmitting the signal. The method of claim 1,
The control unit,
And scheduling to reduce a modulation and coding scheme of any one user of the user pairs by a predetermined value. 5. The method of claim 4,
The control unit,
And scheduling to reset the modulation and coding scheme in consideration of transmission power boosting of any one user of the user pair. As an uplink scheduling method,
a) selecting two users forming a user pair for using the same frequency band among the at least two users transmitting the signal in the same time zone; And
b) performing scheduling to improve the received signal reliability of any one user of the user pairs, uplink scheduling method. The method according to claim 6,
The step b)
Performing scheduling to increase a transmission power strength of any one of the users constituting the user pair by a predetermined value. The method according to claim 6,
The step b)
Scheduling to reset the modulation and coding scheme of any one of the users in the user pair.

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