KR101016720B1 - Feedback controller for mimo communication sysytem - Google Patents

Abstract

PURPOSE: A feedback controller of a MIMO communications system for obtaining an excellent transmission rate performance is provided to operate the communications system based on an MC system. CONSTITUTION: A first effective SNR(Signal to Noise Raito) calculator(222) calculates per-layer effective SNR after multiplexing a pre-coding matrix and a receive channel matrix based on a MC(Multiple Codewords) system. A first transfer rate calculator(226) calculates a first transmission rate. A second transfer calculator calculates the effective SNR after multiplexing the pre-coding matrix and the receive channel matrix based on a SC(Single Codewords) system(230). A second transmission rate output unit(236) produces the second transmission rate.

Description

FEEDBACK CONTROLLER FOR MIMO COMMUNICATION SYSYTEM

The present invention relates to a feedback control apparatus of a MIMO communication system.

Recently, as wireless mobile communication terminals are widely used, various multimedia services have been provided in a wireless environment. In particular, as the capacity of transmission data is increased and data transmission is accelerated, researches on how to efficiently use a limited frequency is being actively conducted, orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple (SC-FDMA) access and multiple input multiple output (MIMO) are the next-generation mobile communication technologies, adopted in the 3GPP LTE standard.

The 3GPP LTE standard defines three types of feedback information: a rank indicator (RI), a channel quality indicator (CQI), and a precoding matrix indicator (PMI). The feedback information is generated according to the channel state information estimated at the receiver, which is transmitted to the transmitter. The transmitter may use the received feedback information to increase channel capacity and data rate or to improve error rate performance. The closed loop MIMO system has a disadvantage in that the complexity of the system increases as the feedback information is generated and transmitted. However, the closed loop MIMO system has the advantage of improving system performance such as data rate and error rate. Therefore, various studies on how to determine feedback information of PMI, CQI, RI, etc. have been preceded.

In relation to a precoding matrix for precoding a transmission symbol vector to have a characteristic that is robust to interference or noise of a MIMO channel, a study of designing an optimal shape of a precoding matrix and a codebook has been preceded. In addition, research has been conducted on a method of generating and using a limited amount of PMI information using a code table of a precoding matrix predefined in a transmitter, or selecting an optimal precoding matrix from a code table according to channel conditions.

In addition, much research has been conducted on CQI information for applying the AMC (adaptive modulation and coding) technique for adjusting the error correction code rate and the modulation scheme order of transmission symbols according to channel conditions. In particular, studies have been conducted to reduce the amount of CQI information fed back and SNR (signal-to-noise ratio) analysis methods for generating CQI information.

However, a study on a method and a criterion for generating and using the three feedback information defined in the LTE standard is unknown. In particular, the use of PMI information has the advantage of improving the BER performance of the system, but it is difficult to apply such a system practically because the probability of occurrence of outage conditions is high in the low SNR region. Therefore, the present invention proposes a MIMO system that can obtain excellent data rate performance while maintaining the probability of occurrence of disabilities required by the system in the entire SNR region.

Some embodiments of the present invention provide a feedback control apparatus of a MIMO communication system for generating and feeding back PMI, CQI, and RI information so as to obtain excellent transmission performance even in a low SNR region.

As a technical means for achieving the above-described technical problem, a first aspect of the present invention is a system for calculating an effective SNR for each layer from a result of multiplying a precoding matrix by a reception channel matrix based on a multiple codewords (MC) system. A first transmission rate for calculating a first transmission rate obtained by adding a product of a code rate and a modulation order of a CQI (channel quality indicator) table corresponding to the effective SNR for each layer calculated by the first effective SNR calculation unit and the first effective SNR calculation unit A second valid SNR calculator for calculating an effective SNR from a result of multiplying the reception channel matrix by the precoding matrix based on a single codewords (SC) system; and an effective calculated through the second valid SNR calculator A second rate calculator for calculating a second rate multiplied by a code rate and a modulation order of a CQI table corresponding to an SNR, and according to the magnitudes of the first rate and the second rate Feedback of the MIMO communication system including a feedback information generation unit for generating RI information, calculating PMI (precoding matrix indicator) information and CQI information at the time of outputting the maximum transmission rate among the calculated transmission rates, and transmitting the information to a transmitting apparatus of the MIMO communication system; Provide a control device.

In addition, the second aspect of the present invention is a first effective SNR calculation unit for calculating the effective SNR for each layer based on a result of multiplying a reception channel matrix by a precoding matrix based on a multiple codewords (MC) system, the first validity A rate calculation unit calculating a first data rate obtained by summing a product of a code rate and a modulation order of a CQI (channel quality indicator) table corresponding to the effective SNR for each layer calculated by the SNR calculation unit, and calculating the first effective SNR calculation unit An RI information generation unit for generating RI information for operating the communication system according to a single codewords (SC) system when any one of effective SNRs for each layer is smaller than a threshold of a channel quality indicator (CQI) table; Search for the maximum data rate among the calculated data rates, calculate precoding matrix indicator (PMI) information and CQI information at the time of outputting the maximum data rate, Provided is a feedback control apparatus for a MIMO communication system including a feedback information generator for transmitting to a transmitter.

According to the above-described problem solving means of the present invention, the communication system is driven based on the SC system in the region where the SNR is low, and the communication system is driven based on the MC system in the other regions. As a result, it is possible to implement a MIMO system that can obtain excellent rate performance while maintaining a constant probability of occurrence in the entire SNR region.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is "connected" to another part, this includes not only "directly connected" but also "electrically connected" with another element in between. . In addition, when a part is said to "include" a certain component, which means that it may further include other components, except to exclude other components unless otherwise stated.

1 is a diagram illustrating a MIMO communication system according to an embodiment of the present invention.

The MIMO communication system 100 includes a transmitting device 110, M transmitting antennas 120, N receiving antennas 130, and a receiving device 140. A closed loop 4 * 2 MIMO system using two codewords is shown.

The transmitting apparatus 110 may perform the modulation according to the encoder 111 encoding the transmission data, the first codeword CW1 and the second codeword CW2, respectively, The layer mapping unit 114 and the precoder 115 are included. The transmitting device 110 performs encoding, modulation, and precoding operations on data to be transmitted using the feedback information PMI, CQI, and RI received from the receiving device 140.

The reception device 140 includes a signal detector 141 for detecting received data from a signal received through the reception antenna 130, a decoder 142 for decoding the detected data and outputting the data, and a reception antenna 130. The feedback control unit 143 generates feedback information (PMI, CQI, RI) from the received signal and transmits it to the transmission device 110. The receiving device 140 may be implemented as a computer or a portable terminal. The computer may include, for example, a laptop, a desktop, a laptop, etc. equipped with a web browser. For example, as a wireless communication device that ensures portability and mobility, Personal Communication System (PCS), Global System for Mobile communications (GSM), Personal Digital Cellular (PDC), Personal Handyphone System (PHS), Personal Digital (PDA) All types of handhelds such as Assistant, International Mobile Telecommunication (IMT) -2000, Code Division Multiple Access (CDMA) -2000, W-Code Division Multiple Access (W-CDMA), and Wireless Broadband Internet (Wibro) terminals ) May include a wireless communication device.

In the LTE standard, three feedback information such as rank indicator (RI) information, channel quality indicator (CQI) information, and precoding matrix indicator (PMI) information are defined for the MIMO communication system 100.

The RI information is information on a rank of the channel matrix. Accordingly, an appropriate transmission scheme is selected from a diversity scheme and a spatial multiplexing scheme. For example, when the RI value is 1, the diversity gain and the code gain may be obtained using the diversity scheme. If the RI value is greater than 1, the data rate may be increased by using a spatial multiplexing method.

The CQI information includes information about a coding rate and a modulation order according to channel state. In practice, the index information of the corresponding CQI table is fed back according to the channel state by using a predefined CQI table for various code rates and modulation order. An example of the CQI table will be described later. In order to generate the CQI table, it is necessary to analyze the frame error rate (FER) performance according to various code rates and modulation orders. Since the signal-to-noise ratio (SNR) section that satisfies the performance required by the system depends on the code rate and modulation order, the appropriate code rate and modulation order are determined for each section. Based on this, the CQI table is generated, and the system searches the CQI table according to the effective SNR of the channel and selects a code rate and modulation order corresponding thereto. In other words, adaptive modulation and coding (AMC) is applied according to channel conditions. In this case, the performance of the system may vary depending on how the effective SNR is defined.

The PMI information includes precoding matrix information according to the channel state. The precoding matrix may be multiplied by a symbol vector mapped to a layer to increase the reliability of data detection while reducing interference between data by a channel. Typically, a single value decomposition (SVD) structure generates an optimal precoding matrix according to a channel state to divide a MIMO channel into a plurality of independent channels. However, a large amount of feedback information is required to generate a complete precoding matrix such as an SVD structure. Therefore, in practice, only the corresponding index of the code table is transmitted by using a predefined codebook. The LTE standard provides a code table of 16 precoding matrices. An example of the code table will be described later.

The method of generating such feedback information may vary depending on the number of codewords used in the MIMO system. The LTE standard supports up to two codewords and can be classified into a single codeword (SC) system and a multiple codewords (MC) system according to the number of codewords. In the SC system, a single codeword is mapped to two transport layers. Although there are two transport layers, since only one codeword is modulated and transmitted, feedback information for a single codeword should be generated instead of feedback information for each layer. Accordingly, it is difficult to generate CQI information determined according to the effective SNR for each layer. On the other hand, in the MC system, the AMC technique may be applied depending on the channel state. The receiver may generate independent CQI information for each codeword according to the effective SNR for each layer. That is, different code rates and orders of modulation schemes can be applied to each code word. Therefore, in the MC system, not only the error rate performance but also the data rate can be improved by using all three kinds of feedback information including CQI information. In the present invention, all three pieces of feedback information can be used based on the MC system.

2 is a diagram illustrating a detailed configuration of a feedback controller of a receiving apparatus according to an embodiment of the present invention.

The feedback controller 140 includes a channel estimator 210, a codebook manager 212, a CQI table storage 214, an MC system 220, an SC system 230, and a feedback information generator 240. . In addition, the MC system 220 includes an effective SNR calculating unit 222, a CQI mapping unit 224, and a rate calculating unit 226, and the SC system 230 includes an effective SNR calculating unit 232 and a CQI mapping unit. 234, a rate calculator 236, and the feedback information generator 240 includes an RI setting unit 242, a maximum rate searcher 244, and an index updater 246. In the present embodiment, the feedback information is generated using the transmission rates calculated by the MC system 220 and the SC system 230.

First, the SC system 230 obtains a reception diversity effect by mapping one codeword to each transport layer in the same manner, and the effective SNR calculating unit 222 calculates an effective SNR through Equation 1 below.

[Equation 1]

Next, the CQI mapping unit 234 determines an appropriate code rate and modulation order based on the calculated effective SNR value and the CQI table stored in the CQI table storage unit 214.

3 is a CQI table stored in a CQI table storage unit according to an embodiment of the present invention.

As shown, a coding rate, a modulation order, and a CQI index may be determined according to a range of valid SNR values. For example, if the calculated effective SNR value is 3, the CQI index is determined to be 2, the code rate is 0.5, and the modulation order is 2.

In particular, in the present invention, even when the effective SNR value is less than -0.5, the code rate and modulation order can be set to zero. In the conventional case, the code rate and the modulation order are not set separately for the case where the effective SNR value is less than -0.5, and even when the effective SNR value is less than -0.5, the code rate and the modulation order are set to 0.33 and 2, respectively. However, there is a problem in that it is impossible to calculate an accurate data rate.

Referring back to FIG. 2, the rate calculator 236 multiplies the code rate determined by the CQI mapping unit 234 and the modulation order to calculate a rate and transmits the rate to the feedback information generator 240.

On the other hand, the MC system 220 is independently applied to the AMC scheme according to the transport layer. That is, the effective SNR calculator 222 calculates an effective SNR for each layer, and determines a code rate and a modulation order for each layer through the CQI mapping unit 224.

The rate calculator 226 calculates a rate by multiplying a code rate calculated for each layer and a modulation order for each layer and then summing them. That is, the transmission rate is calculated through the following equation (2).

[Equation 2]

The RI setting unit 242 of the feedback information generator 240 sets the RI by comparing the transmission rate calculated through the MC system 220 with the transmission rate calculated through the SC system 230. That is, when the transmission rate calculated by the MC system 220 is greater than the transmission rate calculated by the SC system 230, the RI value is set to be larger than 1. However, when the transmission rate calculated by the MC system 220 is smaller than the transmission rate calculated by the SC system 230, the RI value is set to 1 to be switched to the SC system 230.

The maximum rate searching unit 244 searches for the maximum value of the calculated rates. In the present invention, for all precoding matrices, the data rate is repeatedly calculated, and the PMI value and the CQI value when the data rate is maximum are transmitted. To this end, a larger transmission rate is stored by comparing the transmission rate, which was the maximum until the nth stage, with that of the n + 1th stage. This comparison is then repeated for all precoding matrices.

The index updater 246 outputs the CQI index and the PMI index corresponding to the maximum data rate searched by the maximum data rate searcher 244 and transmits the same to the transmitter 110.

For example, as a result of comparing the maximum data rate up to the n th stage with the data rate of the n th +1 stage, if the rate of the n th +1 stage is greater, the index stored in the index updater 246 is converted to the n + 1 th stage. Update to an index for the transfer rate of the step. Then, the rate is recalculated using the precode matrix of the n + 2th step.

However, when the maximum data rate up to the nth stage is larger than the data rate of the n + 1th stage, the data rate is recalculated using the precode matrix of the n + 2th stage without updating the index.

4 is a diagram illustrating a precode matrix stored in a codebook managing unit according to an embodiment of the present invention.

As shown, a total of 16 precode matrices are stored. Accordingly, the process of calculating a data rate, searching for a maximum data rate, and updating an index for the total 16 precode matrices is repeatedly performed.

Meanwhile, the received signal value according to the change of the precoding matrix is calculated through Equation 3.

&Quot; (3) "

를 생성한다. 전송채널 행렬은 수학식 4와 같이 나타낼 수 있다.In this case, x, y, and n are vectors each having a size of 2 × 1 and represent a transmission symbol, a reception symbol, and additional white normal noise, respectively. H is a 2x4 MIMO channel matrix and W represents a 4x2 precoding matrix as described in Table 3. In Equation 3, the multiplication operation of the channel matrix and the precoding matrix is performed using a substantially 2 × 2 transport channel matrix.

. The transport channel matrix may be represented as in Equation 4.

&Quot; (4) "

은 다른 행렬 성분을 가지 게 되고, 그에 따라 시스템의 오류율 성능 및 실제 데이터 전송률이 달라지게 된다. 따라서, 본 발명의 구성에 따라 프리코딩 행렬을 변경함에 따라 오류율 및 전송률 측면에서 최적의 프리코딩 행렬을 탐색할 수 있게 된다.Therefore, the transport channel matrix according to the precoding matrix

Have different matrix components, resulting in different system error rate performance and actual data rates. Accordingly, as the precoding matrix is changed according to the configuration of the present invention, an optimal precoding matrix can be searched in terms of an error rate and a transmission rate.

5 is a diagram illustrating a detailed configuration of a feedback controller of a receiving apparatus according to another embodiment of the present invention.

The feedback controller 140 may include a channel estimator 510, a codebook manager 512, a CQI table storage 514, an effective SNR calculator 520, a CQI mapping unit 522, a rate calculator 524, The RI information generator 530 and the feedback information generator 540 are included.

In the present embodiment, the feedback information is generated based on the MC system. When the RI information is generated, the feedback information is generated by switching to the SC system.

First, the configurations of the effective SNR calculator 520, the CQI mapping unit 522, the rate calculator 524, and the feedback information generator 540 operating based on the MC system are almost the same as those of the embodiment of FIG. 2. .

The RI information generator 530 generates RI information and converts the SC system to the SC system even when the effective SNR value of each layer calculated by the effective SNR calculator 520 does not reach the CQI threshold.

6 is a diagram illustrating a detailed configuration of an RI information generation unit according to an embodiment of the present invention.

The RI information generator 530 includes an RI switching determiner 532, an RI switch 534, and an effective SNR calculator 536. For reference, the components shown in FIGS. 1, 2, 5, and 6 according to an embodiment of the present invention may be software or hardware components such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). It plays a role.

However, 'components' are not meant to be limited to software or hardware, and each component may be configured to be in an addressable storage medium or may be configured to reproduce one or more processors.

Thus, as an example, a component may include components such as software components, object-oriented software components, class components, and task components, and processes, functions, properties, procedures, and subs. Routines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables.

Components and the functionality provided within those components may be combined into a smaller number of components or further separated into additional components.

The RI switching determination unit 532 determines whether the effective SNR value of each layer is greater than the CQI threshold value, and if there is an effective SNR smaller than the CQI threshold value, the RI switching determination unit 534 reports the RI switching unit 534. Through this, RI information for converting the MC system into the SC system is generated. For example, when the MC system is switched to the SC system, RI is set to 1. As described above, even when the MC system is used, when the effective SNR of any layer is smaller than the CQI threshold, the probability of occurrence of the failure is high, thereby deteriorating the error rate performance of the system. Therefore, in such a case, the RI information is generated and the error rate performance is improved by switching from the MC system to the SC system.

One embodiment of the present invention can also be implemented in the form of a recording medium containing instructions executable by a computer, such as a program module executed by the computer. Computer readable media can be any available media that can be accessed by a computer and includes both volatile and nonvolatile media, removable and non-removable media. In addition, computer readable media may include both computer storage media and communication media. Computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Communication media typically includes computer readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave, or other transmission mechanism, and includes any information delivery media.

While the methods and systems of the present invention have been described in connection with specific embodiments, some or all of those elements or operations may be implemented using a computer system having a general purpose hardware architecture.

The foregoing description of the present invention is intended for illustration, and it will be understood by those skilled in the art that the present invention may be easily modified in other specific forms without changing the technical spirit or essential features of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present invention is shown by the following claims rather than the above description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention. do.

1 is a diagram illustrating a MIMO communication system according to an embodiment of the present invention.

2 is a diagram illustrating a detailed configuration of a feedback controller of a receiving apparatus according to an embodiment of the present invention.

3 is a CQI table stored in a CQI table storage unit according to an embodiment of the present invention.

4 is a diagram illustrating a precode matrix stored in a codebook managing unit according to an embodiment of the present invention.

5 is a diagram illustrating a detailed configuration of a feedback controller of a receiving apparatus according to another embodiment of the present invention.

6 is a diagram illustrating a detailed configuration of an RI information generation unit according to an embodiment of the present invention.

Claims (5)

In the feedback control device of a multiple input multiple output (MIMO) communication system, A first effective SNR calculation unit for calculating an effective SNR for each layer based on a result of multiplying a reception channel matrix by a precoding matrix based on an MC (multiple codewords) system, A first data rate calculator for calculating a first data rate obtained by summing a product of a code rate of a channel quality indicator (CQI) table corresponding to the effective SNR for each layer calculated by the first effective SNR calculator and a modulation order; A second effective SNR calculation unit configured to calculate an effective SNR from a result of multiplying the reception channel matrix by the precoding matrix based on a single codewords system; A second rate calculator for calculating a second rate obtained by multiplying a code rate and a modulation order of a CQI table corresponding to the effective SNR calculated by the second effective SNR calculator; RI information is generated according to the magnitudes of the first data rate and the second data rate, and PMI information and CQI information at the maximum data rate output are calculated and transmitted to the transmission apparatus of the MIMO communication system. Feedback information generator Feedback control apparatus of the MIMO communication system comprising a. The method of claim 1, The feedback information generator, An RI setting unit which compares the first data rate with a second data rate and generates RI information for causing the communication system to operate according to the SC system when the first data rate is less than the second data rate; A maximum rate searching unit for searching the maximum rate by comparing the magnitude of the rate calculated by the rate calculating unit with respect to each precoding matrix; An index updater for transmitting the index of the precoding matrix and the index of the CQI table to which the maximum data rate is calculated to the transmitting apparatus Feedback control apparatus of the MIMO communication system comprising a. In the feedback control device of a multiple input multiple output (MIMO) communication system, A first effective SNR calculation unit for calculating an effective SNR for each layer based on a result of multiplying a reception channel matrix by a precoding matrix based on an MC (multiple codewords) system, A rate calculator for calculating a first rate obtained by summing a product of a code rate and a modulation order of a CQI (channel quality indicator) table corresponding to the effective SNR for each layer calculated by the first effective SNR calculator; RI information for allowing the communication system to operate according to a single codewords (SC) system when any one of the effective SNRs for each layer calculated by the first valid SNR calculator is smaller than a threshold value of a channel quality indicator (CQI) table. RI information generation unit for generating a and A feedback information generator for searching for a maximum data rate among the calculated data rates, calculating PMI (precoding matrix indicator) information and CQI information at the time of outputting the maximum data rate, and transmitting the same to a transmitter of the MIMO communication system; Feedback control apparatus of the MIMO communication system comprising a. The method of claim 3, wherein The RI information generator, RI switching determination unit for determining whether the smaller than the minimum SNR stored in the CQI table of the effective SNR for each layer, An RI switching unit configured to generate the RI information so that the communication system operates according to a single codewords system when there is an effective SNR value smaller than the minimum SNR as a result of the determination of the RI switching determination unit; Effective SNR calculation unit for recalculating the effective SNR according to the generated RI information Feedback control apparatus of the MIMO communication system comprising a. The method of claim 3, wherein The feedback information generator, A maximum rate searching unit for searching the maximum rate by comparing the magnitude of the rate calculated by the rate calculating unit with respect to each precoding matrix; An index updater for transmitting the index of the precoding matrix and the index of the CQI table to which the maximum data rate is calculated to the transmitting apparatus Feedback control apparatus of the MIMO communication system comprising a.

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