Precoding method of MIMO-OFDM system and the Precoder thereof

Abstract

A precoding method for a MIMO-OFDM system according to one embodiment of the present invention is characterized by comprising: a step of dividing into N subcarrier groups such that each group includes at least one subcarrier; a step of calculating a precoding matrix for the first subcarrier group and the Nth subcarrier group among the divided N subcarrier groups; a step of performing frequency interpolation on the calculated precoding matrix for the first subcarrier group and the Nth subcarrier group; and a step of calculating a precoding vector by inputting the frequency-interpolated precoding matrix as an initial value to each of the second subcarrier group to the N-1th subcarrier group.

Description

Technology Field

[0001] The present invention relates to a precoding method for a MIMO-OFDM system and a precoder therefor, and in particular, to a precoding method for a MIMO-OFDM system and a precoder therefor that can provide high performance by improving complexity through a reduction in the total amount of iterative computation by receiving and applying an interpolated precoding matrix of an adjacent subcarrier as an initial value when performing iterative precoding of a subcarrier. Background Technology

[0003] Recently, Multiple Input Multiple Output (MIMO) systems have been attracting attention to maximize the performance and capacity of wireless communication systems. MIMO technology is a method that improves data transmission efficiency by adopting multiple transmitting and receiving antennas, departing from the conventional use of a single transmitting and receiving antenna. MIMO systems are also referred to as multiple antenna systems. MIMO technology applies a technique that combines fragmented data received from multiple antennas to complete a single message, rather than relying on a single antenna path to receive the entire message. As a result, it is possible to improve data transmission speeds within a specific range or increase the system coverage for a given data transmission speed.

[0004] MIMO technologies include transmit diversity, spatial multiplexing, and beamforming. Transmit diversity is a technique that enhances transmission reliability by transmitting the same data from multiple transmitting antennas. Spatial multiplexing is a technique that enables high-speed data transmission without increasing system bandwidth by simultaneously transmitting different data from multiple transmitting antennas. Beamforming is used to increase the Signal to Interference plus Noise Ratio (SINR) of signals by applying weights based on channel conditions across multiple antennas. In this context, weights can be represented as weight vectors or weight matrices, which are referred to as precoding vectors or precoding matrices.

[0005] MIMO-OFDM is used as a standard because it provides high channel capacity and can use the same frequency band more efficiently than other modulation techniques.

[0006] In MIMO-OFDM, precoding techniques are a method to effectively reduce SINR at the receiver. Generally, among linear precodings, Zero-Forcing (ZF) shows optimal performance, but since direct inverse matrix calculation is complex, precodings that provide low complexity through iterative linear operations, such as Successive Over Relaxation (SOR), have been proposed.

[0007] In MIMO-OFDM, performing precoding for each individual subcarrier provides high performance in most situations, but the complexity is very high because there are at least 120 subcarriers. Complexity can be reduced by grouping multiple subcarriers together and performing precoding in batches, but performance degradation becomes significant as the ratio of the number of receiving antennas to the number of transmitting antennas increases.

[0008] Therefore, research is needed to optimize precoding algorithms based on subcarriers to achieve high performance with low computational complexity. The problem to be solved

[0010] To solve the aforementioned problem, a precoding method for a MIMO-OFDM system and a precoder therefor are provided, which can provide high performance by improving complexity through a reduction in the total amount of iterative computation by receiving and applying an interpolated precoding matrix of an adjacent subcarrier as an initial value when performing iterative precoding of a subcarrier.

[0011] However, the technical problems that the present invention aims to solve are not limited to those described above, and other unmentioned problems will be clearly understood by those skilled in the art from the description of the invention below. means of solving the problem

[0013] A precoding method for a MIMO-OFDM system according to one embodiment of the present invention is characterized by comprising: a step of dividing into N subcarrier groups such that each group includes at least one subcarrier; a step of calculating a precoding matrix for the first subcarrier group and the Nth subcarrier group among the divided N subcarrier groups; a step of performing frequency interpolation on the calculated precoding matrix for the first subcarrier group and the Nth subcarrier group; and a step of calculating a precoding vector by inputting the frequency-interpolated precoding matrix as an initial value to each of the second subcarrier group to the N-1th subcarrier group.

[0014] Here, in particular, the step of calculating the precoding matrix is ​​characterized by applying a Successive Over Relaxation (SOR) algorithm to the channel matrix (H) of the first subcarrier group and the Nth subcarrier group and the transmit vector(s) as inputs to calculate the precoding matrix.

[0015] Here, in particular, the precoding matrix is ​​characterized by the fact that it is calculated using the following mathematical formula 1.

[0016] [Mathematical Formula 1]

[0017] Here, W is the precoding matrix, R is the iteration matrix coefficient, C is the constant coefficient, is the number of repetitions.

[0019] Here, the invention is characterized in that, particularly in the step of performing frequency interpolation, the precoding matrix (W) of the calculated first subcarrier group and the Nth subcarrier group is interpolated by applying a linear interpolation method in the frequency direction.

[0020] Here, in particular, the feature is that in the step of calculating the precoding vector, each subcarrier group in the second subcarrier group to the N-1st subcarrier group inputs a precoding matrix and a respective channel matrix (H) as initial values ​​and repeatedly calculates the precoding vector.

[0021] Here, in particular, the above-mentioned precoding vector is characterized by being calculated using the following mathematical formula 2.

[0022] [Mathematical Formula 2]

[0023] Here, x is the precoding vector, R is the iteration matrix coefficient, and C is the constant coefficient.

[0024] Here, in particular, the process of iteratively calculating the precoding vector is characterized by the fact that the process terminates after iteratively calculating the precoding vector for each group from the second subcarrier group to the N-1th subcarrier group, for a number of times equal to the number of subcarriers in each group.

[0025] In addition, the precoder of a MIMO-OFDM system according to one embodiment of the present invention is characterized by comprising: a distribution unit that divides into N subcarrier groups each containing at least one subcarrier; a precoding matrix generation unit that calculates a precoding matrix for the first subcarrier group and the Nth subcarrier group among the divided N subcarrier groups; an interpolation unit that performs frequency interpolation on the calculated precoding matrix for the first subcarrier group and the Nth subcarrier group; and a precoding vector generation unit that calculates a precoding vector by inputting the frequency-interpolated precoding matrix as an initial value to each of the second subcarrier group to the N-1th subcarrier group.

[0026] Here, in particular, the precoding matrix generation unit is characterized by calculating a precoding matrix by applying a Successive Over Relaxation (SOR) algorithm to the channel matrix (H) of the first subcarrier group and the Nth subcarrier group and the transmission vector(s) as inputs.

[0027] Here, in particular, the precoding matrix is ​​characterized by the fact that it is calculated using the following mathematical formula 1.

[0028] [Mathematical Formula 1]

[0029] Here, W is the precoding matrix, R is the iteration matrix coefficient, C is the constant coefficient, is the number of repetitions.

[0030] Here, in particular, the interpolation unit is characterized by performing interpolation by applying a linear interpolation method in the frequency direction to the precoding matrix (W) of the calculated first subcarrier group and the Nth subcarrier group.

[0031] Here, in particular, the precoding vector generation unit is characterized by the fact that, in the second subcarrier group to the N-1th subcarrier group, each subcarrier group inputs a precoding matrix and a respective channel matrix (H) as initial values ​​and repeatedly calculates a precoding vector.

[0032] Here, in particular, the above-mentioned precoding vector is characterized by being calculated using the following mathematical formula 2.

[0033] [Mathematical Formula 2]

[0034] Here, x is the precoding vector, R is the iteration matrix coefficient, and C is the constant coefficient.

[0035] Here, in particular, the process of iteratively calculating the precoding vector is characterized by the fact that the process terminates after iteratively calculating the precoding vector for each group from the second subcarrier group to the N-1th subcarrier group, for a number of times equal to the number of subcarriers in each group. Effects of the invention

[0037] According to one embodiment of the present invention described above, when performing iterative precoding of a subcarrier, high performance can be provided by improving complexity through a reduction in the total amount of iterative computation by receiving and applying an interpolated precoding matrix of an adjacent subcarrier as an initial value.

[0038] However, the effects obtainable through the present invention are not limited to those described above, and other unmentioned technical effects will be clearly understood by those skilled in the art from the description of the invention below. Brief explanation of the drawing

[0040] FIG. 1 is a schematic diagram illustrating the configuration of a transmitting device of a MIMO-OFDM system according to one embodiment of the present invention. FIG. 2 is a schematic diagram illustrating the configuration of a precorder of the MIMO-OFDM system of the present invention. FIG. 3 is a diagram visualizing the structure of the precoder algorithm of the MIMO-OFDM system of the present invention. FIG. 4 is a flowchart schematically illustrating a precoding method of a MIMO-OFDM system according to an embodiment of the present invention. FIG. 5 is a flowchart for the MIMO-OFDM precoding algorithm of FIG. 4. FIGS. 6 and FIGS. 7 are drawings showing the results of comparison for cases where the ratio of the number of receiving antennas to the number of transmitting antennas of the present invention is different. FIG. 8 is a diagram showing the results of analyzing and comparing the computational complexity of the present invention and the types of computational complexity of the prior art. FIG. 9 is a diagram showing the results of a comparison of the computational complexity of the precoding algorithm of the present invention and the prior art at M=32. Specific details for implementing the invention

[0041] The present invention is susceptible to various modifications and may have various embodiments, and specific embodiments will be described in detail with reference to the drawings. However, this is not intended to limit the invention to specific embodiments, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention. Similar reference numerals have been used for similar components in the description of each drawing.

[0042] Terms such as first, second, A, B, etc., may be used to describe various components, but said components shall not be limited by said terms. These terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be named the second component, and similarly, the second component may be named the first component. The term "and / or" includes a combination of multiple related description items or any of the multiple related description items.

[0043] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "having" are intended to indicate the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0044] Throughout the specification and claims, when a part is described as including a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0046] FIG. 1 is a schematic diagram illustrating the configuration of a transmitting device of a MIMO-OFDM system according to one embodiment of the present invention, FIG. 2 is a schematic diagram illustrating the configuration of a precoder of a MIMO-OFDM system of the present invention, and FIG. 3 is a diagram visualizing the structure of a precoder algorithm of a MIMO-OFDM system of the present invention.

[0048] As illustrated in FIG. 1, the MIMO-OFDM communication system (1) of the present invention comprises a transmitting device (10), a MIMO communication channel (20), and a receiving device (30). The transmitting device (10) may be, for example, a base station of a cellular telephony network (e.g., following the LTE standard), and the receiving device may be a User Equipment (UE). Here, the wireless communication system may be an OFDM (Orthogonal Frequency Division Multiplexing) / OFDMA (Orthogonal Frequency Division Multiple Access) based system. OFDM utilizes multiple orthogonal subcarriers. OFDM utilizes the orthogonality characteristics between the IFFT (inverse fast Fourier Transform) and the FFT (fast Fourier Transform). The transmitting device performs an IFFT on the data and transmits it. The receiver performs an FFT on the received signal to restore the original data. The transmitter uses an IFFT to combine multiple subcarriers, and the receiver uses a corresponding FFT to separate the multiple subcarriers.

[0049] Additionally, the transmitting device (10) includes an encoder (100), a modulator (200), a layer mapper (300), a precoder (400), a subcarrier mapper (500), an OFDM signal generator (600), and Nt (Nt≥1) transmitting antennas (700).

[0050] The encoder (100) forms coded data by encoding input data according to a predetermined coding method. Here, the coded data is referred to as a codeword.

[0051] The modulator (200) arranges the codeword into symbols representing positions on the signal constellation. There are no restrictions on the modulation scheme and it may be m-PSK (m-Phase Shift Keying) or m-QAM (m-Quadrature Amplitude Modulation). For example, m-PSK may be BPSK, QPSK, or 8-PSK. m-QAM may be 16-QAM, 64-QAM, or 256-QAM.

[0052] The layer mapper (300) defines a layer of input symbols so that the precoder (400) can distribute antenna-specific symbols to the paths of each antenna. The layer is defined as an information path input to the precoder (140).

[0053] The information path prior to the precoder (400) can be referred to as a virtual antenna or a layer. The precoder (400) processes input symbols using a MIMO method according to multiple transmission antennas (700). For example, the precoder (400) may use codebook-based precoding. The precoder (400) distributes antenna-specific symbols to subcarrier mappers (500) of the path of the corresponding antenna. Each information path sent to one antenna through one subcarrier mapper by the precoder (400) is referred to as a stream. This can be referred to as a physical antenna.

[0054] The subcarrier mapper (500) assigns the input symbol to an appropriate subcarrier and multiplexes it according to the user. The OFDM signal generator (600) modulates the input symbol in the OFDM manner and outputs an OFDM symbol. The OFDM signal generator (600) can perform an Inverse Fast Fourier Transform (IFFT) on the input symbol, and a cyclic prefix (CP) can be inserted into the time-domain symbol after the IFFT is performed. The OFDM symbol is transmitted through each transmitting antenna (700).

[0055] In the aforementioned MIMO-OFDM, performing precoding for each individual subcarrier provides high performance in most situations, but since the number of subcarriers is at least 120, the complexity is very high, so multiple subcarriers are grouped together to perform precoding collectively. Therefore, as the ratio of the number of receiving antennas to the number of transmitting antennas increases, performance degradation is significant. Accordingly, we will describe the precoder of the present invention, which can provide low computational complexity by optimizing the precoding algorithm according to the subcarriers.

[0057] As illustrated in FIG. 2, a precoder (400) of a MIMO-OFDM system according to one embodiment of the present invention comprises a distribution unit (410), a precoding matrix generation unit (420), an interpolation unit (430), and a precoding vector generation unit (440).

[0059] The distribution unit (410) is divided into N subcarrier groups to include at least one subcarrier. For example, each subcarrier group may be configured to include 10 subcarriers, but is not limited thereto and may be configured in various ways.

[0061] The precoding matrix generation unit (420) calculates the precoding matrix of the first subcarrier group and the Nth subcarrier group among the divided N subcarrier groups. Here, the precoding matrix generation unit (420) calculates the precoding matrix by applying a Successive Over Relaxation (SOR) algorithm to the channel matrix (H) of the first subcarrier group and the Nth subcarrier group and the transmission vector (s) as inputs. At this time, the precoding matrix can be calculated using the following mathematical formula 1.

[0062] [Mathematical Formula 1]

[0063]

[0064] Here, W is the precoding matrix, R is the iteration matrix coefficient, C is the constant coefficient, is the number of repetitions.

[0066] The interpolation unit (430) performs frequency interpolation on the precoding matrices of the first subcarrier group and the Nth subcarrier group calculated above. Here, the interpolation unit (430) performs interpolation by applying a linear interpolation method in the frequency direction to the precoding matrices (W) of the first subcarrier group and the Nth subcarrier group calculated above.

[0067] The precoding vector generation unit (440) calculates a precoding vector by inputting the frequency-interpolated precoding matrix as an initial value to each of the second subcarrier group to the N-1st subcarrier group. Here, the precoding vector generation unit (440) repeatedly calculates a precoding vector by inputting the precoding matrix and each channel matrix (H) as initial values ​​to each of the subcarrier groups from the second subcarrier group to the N-1st subcarrier group. Then, in the process of repeatedly calculating the precoding vector, the precoding vector is calculated repeatedly as many times as the number of subcarriers in each group from the second subcarrier group to the N-1st subcarrier group, and then terminates.

[0068] At this time, the above precoding vector is calculated using the following mathematical formula 2.

[0069] [Mathematical Formula 2]

[0070]

[0071] Here, x is the precoding vector, R is the iteration matrix coefficient, and C is the constant coefficient.

[0072] In other words, as illustrated in Fig. 3, precoding is performed in units of subcarrier bundles divided into Ng, and precoding is first performed by repeating pi times on the co-carriers at both ends; however, this is not to obtain the precoding transmission vector, but to calculate the precoding transmission matrix. Therefore, when interpolating the calculated precoding matrix, the interpolation is performed by multiplying each given constant according to the Ng value and adding them. The interpolated matrix is ​​precoded repeatedly si times using their respective channel matrices on each subcarrier, which is a process to obtain the precoding transmission vector, and the algorithm terminates when precoding has been performed for all subcarriers Nsc.

[0074] In addition, FIG. 4 is a flowchart schematically illustrating a precoding method of a MIMO-OFDM system according to an embodiment of the present invention, and FIG. 5 is a flowchart for the MIMO-OFDM precoding algorithm of FIG. 4.

[0076] As illustrated in FIG. 4, a precoding method for a MIMO-OFDM system according to one embodiment of the present invention first performs the step of dividing into N subcarrier groups, each including at least one subcarrier (S410). For example, each subcarrier group may be configured to include 10 subcarriers, but is not limited thereto and may be configured in various ways.

[0078] Next, a step of calculating the precoding matrix of the first subcarrier group and the Nth subcarrier group among the N subcarrier groups divided above is performed (S420).

[0079] More specifically, the precoding matrix is ​​calculated by applying the Successive Over Relaxation (SOR) algorithm to the channel matrix (H) of the first subcarrier group and the Nth subcarrier group and the transmit vector(s) as inputs. At this time, the precoding matrix is ​​calculated using the following Equation 1.

[0080] [Mathematical Formula 1]

[0081]

[0082] Here, W is the precoding matrix, R is the iteration matrix coefficient, C is the constant coefficient, is the number of repetitions.

[0084] Then, a step of performing frequency interpolation on the precoding matrices of the first subcarrier group and the Nth subcarrier group calculated above is performed (S430).

[0085] Here, the frequency interpolation is performed by applying a linear interpolation method in the frequency direction to the precoding matrix (W) of the calculated first subcarrier group and the Nth subcarrier group.

[0087] Next, the frequency-interpolated precoding matrix is ​​input as an initial value to each of the second subcarrier group to the N-1th subcarrier group to calculate a precoding vector (S440).

[0088] More specifically, the calculation of the precoding vectors is performed by iteratively calculating the precoding vectors in each subcarrier group from the second subcarrier group to the N-1th subcarrier group by inputting the precoding matrix and each channel matrix (H) as initial values. Here, the precoding vectors are calculated using the following Equation 2.

[0089] [Mathematical Formula 2]

[0090]

[0091] Here, x is the precoding vector, R is the iteration matrix coefficient, and C is the constant coefficient.

[0092] At this time, during the process of repeatedly calculating the precoding vector, the process terminates after repeatedly calculating the precoding vector for each group from the second subcarrier group to the N-1th subcarrier group as many times as the number of subcarriers in each group.

[0094] Meanwhile, the SOR (Successive Over Relaxation) precoder algorithm can be performed as follows, and refer to the flowchart in Fig. 5.

[0096]

[0097] As shown in Fig. 5, the gram matrix for each channel, the signal to be sent from each subcarrier, and the attenuation factor are input, and the precoded signal is output. First, the precoding matrix is ​​calculated using the SOR method for some equally spaced subcarriers. This is interpolated in the frequency direction, and the additional SOR precoding iteration is performed on each subcarrier using the interpolated matrix. That is, by sharing the precoding matrix and interpolating it, the shared subcarrier receives a matrix that is highly similar to its own precoding matrix. This allows for much faster convergence than performing the SOR precoding iteration using its own channel matrix from the beginning.

[0098] Therefore, since the number of iterations of the subcarrier sharing the precoding matrix is ​​reduced, the total number of iterations of MIMO-OFDM precoding can be effectively reduced.

[0100] Meanwhile, FIGS. 6 and 7 are drawings showing the results of a comparison for cases where the ratio of the number of receiving antennas to the number of transmitting antennas of the present invention is different, and FIGS. 8 and 9 are drawings showing the results of a comparison of the computational complexity of the present invention.

[0102] As shown in Fig. 6, the precoding performance was compared in a situation where the receiving antenna M=32 and the transmitting antenna K=8, and as shown in Fig. 7, the precoding performance was compared in a situation where the receiving antenna M=32 and the transmitting antenna K=16. That is, the results of comparing the conventional algorithm and the algorithm of the present invention for cases where the ratio of the number of receiving antennas to the number of transmitting antennas is different. In this case, ZF-per-subcarrier refers to the most optimal precoding where ZF precoding is performed for each subcarrier. SOR-shared-10 is an algorithm in the algorithm of the present invention that performs precoding by grouping subcarriers in units of 10 without interpolation in the frequency direction, and interp-10 is an algorithm that calculates the precoding matrix in units of 10 and then interpolates in the frequency direction. Although this interpolation algorithm has very low complexity, it can be seen that the Uncoded SER performance degrades by more than 1,000 times compared to ZF as the number of receiving antennas increases. It can be seen through SOR-shared that the precoding sharing method of the algorithm of the present invention yields better performance than the conventional interpolation method, but does not reach the performance of optimal precoding. However, it can be confirmed that combining frequency direction interpolation with the precoding matrix sharing method demonstrates performance nearly similar to optimal precoding.

[0104] FIG. 8 is a diagram showing the results of analyzing and comparing the computational complexity of the present invention and the types of computational complexity of the prior art, and FIG. 9 is a diagram showing the results of comparing the computational complexity of the precoding algorithm of the present invention and the prior art at M=32.

[0106] In addition, as shown in Fig. 8, as a detailed comparison indicator of the number of operations with the prior art, the number of iterations for the SOR algorithm is set to 14 times, and for the algorithm of the present invention, the number of iterations for the sharer is set to 10 times and for the shared recipient to 4 times so that the prior art and the algorithm of the present invention exhibit the same performance. Since the calculation of the matrices R and C required for the iteration algorithm must be performed for all subcarrier channels, it shows the same complexity, but it shows significant improvement in the algorithm iteration part. It can be seen that the total number of operations is effectively reduced because the number of precoding iterations performed on 10 shared subcarriers has decreased from 14 times to 10 times compared to the prior art, and the number of precoding iterations performed on the remaining 110 shared subcarriers has decreased significantly from 14 times to 4 times compared to the prior art. Accordingly, a computational complexity of 31.1% can be confirmed in the algorithm iteration part excluding R and C calculations, and an improvement of 25.4% in the overall complexity can be confirmed.

[0107] In addition, as shown in FIG. 9, a comparison with the prior art of a linear precoding algorithm is shown when the number of transmitting antennas is fixed at 32. Through FIG. 9, it can be confirmed that the complexity is lower than that of the prior art for various numbers of receiving antennas, and when the number of receiving antennas is 16, which is the purpose of the present invention, it shows a complexity improved by 40.8% compared to ZF, which shows optimal precoding performance.

[0109] Accordingly, according to the present invention described above, although it is very difficult to apply to OFDM due to the high complexity of MIMO OFDM precoding, it is advantageous to apply it to actual communication systems because the amount of computation is reduced by providing an interpolated precoding matrix as the initial value of the precoding algorithm. In addition, since an effective reduction in the amount of computation is achieved simply by setting the initial value well without modifying the iterative precoding algorithm, it becomes possible to apply iterative precoding algorithms other than SOR.

[0110] One embodiment of the present invention may also be implemented in the form of a recording medium containing computer-executable instructions, such as program modules executed by a computer. A computer-readable medium may be any available medium accessible by a computer and includes both volatile and non-volatile media, and both removable and non-removable media. Additionally, a computer-readable medium may include both computer storage media and communication media. A computer storage medium includes both volatile and non-volatile, removable and non-removable media implemented by any method or technique for storing information, such as computer-readable instructions, data structures, program modules, or other data. A communication medium typically includes computer-readable instructions, data structures, program modules, or other data of modulated data signals such as carrier waves, or other transmission mechanisms, and includes any information transmission medium.

[0111] Although the method and system of the present invention have been described in relation to specific embodiments, some or all of their components or operations may be implemented using a computer system having a general-purpose hardware architecture.

[0112] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0113] The scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention. Explanation of the symbols

[0115] 10 : Transmitter 20: MIMO communication channel 30: Receiver 100: Encoder 200: Modulator 300: Hierarchy Mapper 400: Precorder 500: Subcarrier mapper 600: OFDM signal generator 700: Transmitting antenna 410: Distribution section 420: Precoding Matrix Generation Unit 430: Cadre 440: Precoding Vector Generation Unit

Claims

Claim 1 A precoding method for a MIMO-OFDM system comprising: a step of dividing into N subcarrier groups each containing at least one subcarrier; a step of calculating a precoding matrix for a first subcarrier group and an Nth subcarrier group among the divided N subcarrier groups; a step of performing frequency interpolation on the calculated precoding matrix for the first subcarrier group and the Nth subcarrier group; and a step of calculating a precoding vector by inputting the frequency-interpolated precoding matrix as an initial value to each of the second subcarrier group to the N-1th subcarrier group. Claim 2 A precoding method for a MIMO-OFDM system according to claim 1, wherein the step of calculating the precoding matrix is ​​characterized by applying a Successive Over Relaxation (SOR) algorithm to the channel matrix (H) of the first subcarrier group and the Nth subcarrier group and the transmission vector(s) as inputs to calculate the precoding matrix. Claim 3 A precoding method for a MIMO-OFDM system according to claim 2, characterized in that the precoding matrix is ​​calculated using the following mathematical formula 1.[Mathematical Formula 1] Here, W is the precoding matrix, R is the iteration matrix coefficient, C is the constant coefficient, is the number of repetitions. Claim 4 A precoding method for a MIMO-OFDM system according to claim 1, characterized in that, in the step of performing frequency interpolation, the precoding matrix (W) of the calculated first subcarrier group and the Nth subcarrier group is interpolated by applying a linear interpolation method in the frequency direction. Claim 5 A precoding method for a MIMO-OFDM system according to claim 1, characterized in that, in the step of calculating the precoding vector, each subcarrier group in the second subcarrier group to the N-1st subcarrier group inputs a precoding matrix and each channel matrix (H) as initial values ​​and repeatedly calculates the precoding vector. Claim 6 A precoding method for a MIMO-OFDM system according to claim 5, characterized in that the precoding vector is calculated using the following mathematical formula 2.[Mathematical Formula 2] Here, x is the precoding vector, R is the iteration matrix coefficient, and C is the constant coefficient. Claim 7 A precoding method for a MIMO-OFDM system according to claim 5, characterized in that, in the process of repeatedly calculating the precoding vector, the precoding vector is repeatedly calculated for each group of the second subcarrier group to the N-1st subcarrier group, and then terminated. Claim 8 A precoder of a MIMO-OFDM system comprising: a distribution unit that divides into N subcarrier groups each containing at least one subcarrier; a precoding matrix generation unit that calculates a precoding matrix for a first subcarrier group and an Nth subcarrier group among the divided N subcarrier groups; an interpolation unit that performs frequency interpolation on the calculated precoding matrix for the first subcarrier group and the Nth subcarrier group; and a precoding vector generation unit that calculates a precoding vector by inputting the frequency-interpolated precoding matrix as an initial value to each of the second subcarrier group to the N-1th subcarrier group. Claim 9 A precoder of a MIMO-OFDM system according to claim 8, wherein the precoding matrix generation unit calculates a precoding matrix by applying a SOR (Successive Over Relaxation) algorithm to the channel matrix (H) of the first subcarrier group and the Nth subcarrier group and the transmission vector(s) as inputs. Claim 10 A precoder of a MIMO-OFDM system according to claim 9, characterized in that the precoding matrix is ​​calculated using the following mathematical formula 1.[Mathematical Formula 1] Here, W is the precoding matrix, R is the iteration matrix coefficient, C is the constant coefficient, is the number of repetitions. Claim 11 A precoder of a MIMO-OFDM system according to claim 8, wherein the interpolation unit performs interpolation by applying a linear interpolation method in the frequency direction to the precoding matrix (W) of the calculated first subcarrier group and the Nth subcarrier group. Claim 12 A precoder of a MIMO-OFDM system according to claim 8, wherein the precoding vector generation unit is characterized by repeatedly calculating a precoding vector by inputting a precoding matrix and a channel matrix (H) as initial values ​​to each subcarrier group in the second subcarrier group to the N-1st subcarrier group. Claim 13 A precoder of a MIMO-OFDM system according to claim 12, characterized in that the precoding vector is calculated using the following mathematical formula 2.[Mathematical Formula 2] Here, x is the precoding vector, R is the iteration matrix coefficient, and C is the constant coefficient. Claim 14 A precoder of a MIMO-OFDM system according to claim 12, characterized in that, in the process of repeatedly calculating the precoding vector, the process terminates after repeatedly calculating the precoding vector for each group from the second subcarrier group to the N-1st subcarrier group as many times as the number of subcarriers in each group.

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