WO2008111810A1

WO2008111810A1 - Method for transmitting/receiving a signal and apparatus for transmitting/receiving a signal

Info

Publication number: WO2008111810A1
Application number: PCT/KR2008/001427
Authority: WO
Inventors: Woo Suk Ko; Sang Chul Moon
Original assignee: Lg Electronics Inc.
Priority date: 2007-03-13
Filing date: 2008-03-13
Publication date: 2008-09-18

Abstract

A method and apparatus for transmitting and receiving signals is disclosed. When data is carried on subcarriers to be transmitted, the data can be spread through precoding before being transmitted in order to prevent data carried on subcarriers of a specific frequency from being lost by frequency selective fading. Since data is precoded for transmission, channels in various channel environments do not affect the data and the correlation between channels is reduced, thereby increasing the performance of receiving signals.

Description

METHOD FOR TRANSMITTING/RECEIVING A SIGNAL AND APPARATUS FOR TRANSMITTING/RECEIVING A SIGNAL

Technical Field

[1] The present invention relates to a method for transmitting and receiving signals and an apparatus for transmitting and receiving signals. Background Art

[2] According to an Orthogonal Frequency Division Multiplexing (OFDM) scheme which is a method for modulating signals, multiple symbols are transmitted simultaneously through multiple transmission bands, each having a very narrow bandwidth. That is, the OFDM scheme is a multicarrier transmission method with a high spectral efficiency, which divides a broadband signal into orthogonal subcarriers of narrow bands and simultaneously transmits them overlapping each other.

[3] If a single-carrier scheme is used when high-rate data with a short symbol period is transmitted over a wireless communication channel exhibiting multipath fading, inter- symbol interference is high, thereby increasing the complexity of the receiving end. However, if a multi-carrier scheme is applied, it is possible to increase the symbol period of each subcarrier by the number of subcarriers while keeping the data transfer rate constant, thereby reducing relative signal distribution in the time domain caused by multipath delay spread. Thus, modulating signals using the OFDM scheme allows the signals to be robust to synchronization errors in the time domain or channel delays.

[4] According to the OFDM scheme, guard intervals longer than a channel delay spread are inserted between OFDM symbols to remove inter-symbol interference. However, transmission channels having a long delay time exhibit selective fading in the frequency domain and undergo serious size distortion due to channel delay spread. Thus, the OFDM scheme has problems in that the Signal to Noise Ratio (SNR) of each transmission band is different and the reception rate is reduced for transmission channels with a low SNR.

[5] Although the amount of data desired by users is on the rise due to technological development, there are limitations on extension of transmission resources for transmitting data to users. Accordingly, a variety of technologies have been developed to increase the transmission efficiency of data using limited transmission resources.

[6] Such technologies include a signal transmission scheme which increases the efficiency of signal transmission using multiple transmit/receive antennas. One example of the transmission scheme is a Multi- Input Multi-Output (MIMO) scheme.

[7] Basically, the performance of a MIMO system depends on the characteristics of transport channels. The performance of the MIMO system increases as the correlation between channels established between antennas at the transmitting end and antennas at the receiving end decreases (i.e., as the independence of the channels increases). That is, the MIMO system may be significantly reduced in performance or may be inoperable in a channel environment such as a Line-Of-Sight (LOS) environment where the correlation between channels established between transmit and receive antennas is very high.

[8] In mobile communication network environments such as the Wireless Broadband

Internet (Wibro) or 3rd Generation Partnership Project (3GPP), it is generally possible to perform two-way communication between a transmitting base station and user terminals. In such mobile communication systems, the transmitting base station or the user terminal constantly monitors channel states of downlink (from the base station to the terminal) and uplink (from the terminal to the base station) and the base station takes appropriate measures when a channel environment unsuitable for MIMO such as the LOS environment is detected.

[9] This dynamic adaptation technique is required to increase the performance of the

MIMO system. However, it is not possible to apply channel monitoring and an adaptation technique according to the monitoring in system environments without an uplink established from the user terminal to the transmitting base station, unlike system environments with the uplink.

[10] Dual polarization diversity can be used as a scheme robust to channel environments with a high correlation between channels such as the LOS environment. This scheme reduces the correlation between channels using transmission signals of vertical and horizontal polarities. Even in the LOS environment, the dual polarization diversity scheme maintains low correlation and exhibits improved performance compared to other systems.

[11] However, applying the dual polarization diversity scheme generally reduces receiving performance in channel environments favorable for the MIMO system. Disclosure of Invention Technical Problem

[12] An object of the present invention devised to solve the problem lies in providing a method and apparatus for transmitting and receiving signals wherein a coding gain is obtained so that the signals are robust to frequency selective fading.

[13] Another object of the present invention devised to solve the problem lies in providing a method and apparatus for transmitting and receiving signals wherein a coding gain is obtained so that channels in various channel environments do not affect the signals. Technical Solution

[14] The object of the present invention can be achieved by providing an apparatus for transmitting signals, the apparatus including a precoder for precoding input data; a frame builder for converting data output from the precoder into a time domain, inserting a guard interval into a valid data section converted into the time domain to generate a transmission symbol, and cumulating transmission symbols to create a frame; a modulator for modulating data of the frame; and a transmission unit for converting the modulated data into analog data and transmitting the analog data.

[15] The precoder may multiply the arranged data elements by a Vandermonde matrix and output the multiplied data elements.

[16] The precoder may precode and output the input data to multiple paths.

[17] The precoder may precode the input data using a golden code when a spatial multiplexing scheme is used as a Multi-Input Multi-Output (MIMO) scheme.

[18] The precoder may precode the input data using a Space Time Trellis Code (STTC) when a spatial diversity scheme is used as a MIMO scheme.

[19] The transmission unit may convert the modulated data into analog data according to a dual polarization diversity scheme and transmit the analog data.

[20] A method for transmitting signals according to an embodiment of the invention may include precoding input data; converting the precoded data into a time domain, inserting a guard interval into a valid data section converted into the time domain to generate a modulation symbol, and cumulating generated modulation symbols to create a frame; modulating data of the created frame; and converting the modulated data into analog data and transmitting the analog data.

[21] An apparatus for receiving signals according to an embodiment of the invention may include a reception unit for converting received analog data into digital data; a synchronizer for restoring synchronization of the digital data; a demodulator for demodulating the data whose synchronization has been restored; a frame parser for parsing the demodulated data in a frequency domain and outputting symbol data in a valid data section; and a precoding decoder for decoding the symbol data according to reverse precoding and outputting a symbol data sequence.

[22] The reception unit may convert received analog data into digital data according to a dual polarization diversity scheme.

[23] When a spatial multiplexing scheme is used as a Multi-Input Multi-Output (MIMO) scheme, the precoding decoder may decode received data according to a Maximum Likelihood (ML) method and perform de-matrixing on the decoded data according to a reverse golden code to reconstruct symbol data as before precoding.

[24] When a spatial diversity scheme is used as a MIMO scheme, the precoding decoder may decode received data in a Maximum Likelihood (ML) method to reconstruct symbol data as before precoding. [25] A method for receiving signals according to an embodiment of the invention may include converting received analog data into digital data; restoring synchronization of the digital data; demodulating the data whose synchronization has been restored; parsing the demodulated data in a frequency domain and outputting symbol data in a valid data section; and decoding the symbol data according to reverse precoding and outputting a symbol data sequence. [26] The above and other objects, features and other advantages of the invention will be clearly understood from the following detailed description taken in conjunction with the accompanying drawings.

Advantageous Effects

[27] The method and apparatus for transmitting and receiving signals according to the invention has the following advantages. According to the invention, signals can be modulated and transmitted so that they are robust to frequency selective fading and modulated signals can also be received so that they are robust to frequency selective fading. According to the invention, channels in various channel environments do not affect signals and the correlation between channels is reduced, thereby increasing the performance of receiving signals. Brief Description of the Drawings

[28] FIG. 1 illustrates an example method in which input data is precoded to spread the input data;

[29] FIG. 2 is a detailed block diagram of a signal transmitter according to an embodiment of the invention;

[30] FIG. 3 illustrates detailed examples of a precoder and a frame builder shown in

FIG. 2;

[31] FIG. 4 is a detailed block diagram of a signal receiver according to an embodiment of the invention;

[32] FIG. 5 is a flow chart of a method for transmitting and receiving signals according to the invention;

[33] FIG. 6 schematically illustrates a transceiver system where precoding is applied in a spatial multiplexing scheme according to another embodiment of the invention;

[34] FIG. 7 illustrates a code for precoding in the spatial multiplexing scheme according to another embodiment of the invention;

[35] FIG. 8 schematically illustrates a transceiver system where precoding is applied in a spatial diversity scheme according to another embodiment of the invention;

[36] FIG. 9 illustrates a code for precoding in the spatial diversity scheme according to another embodiment of the invention;

[37] FIG. 10 is a detailed block diagram of a signal transmitter using precoding according to another embodiment of the invention;

[38] FIG. 11 is a detailed block diagram of a signal receiver using precoding according to another embodiment of the invention;

[39] FIG. 12 is a detailed block diagram of a signal transmitter using precoding according to another embodiment of the invention;

[40] FIG. 13 is a detailed block diagram of a signal receiver using precoding according to another embodiment of the invention; and

[41] FIG. 14 is a flow chart of a method for transmitting and receiving signals using precoding according to another embodiment of the invention. Best Mode for Carrying Out the Invention

[42] Preferred embodiments of the invention, which can achieve the above objects, will now be described with reference to the accompanying drawings. The configuration and operation of the invention, illustrated in the drawings and described below with reference to the drawings, will be described using at least one embodiment without limiting the spirit and the essential configuration and operation of the invention.

[43] Although most terms of elements in the present invention have been selected from general ones widely used in the art taking into consideration their functions in the invention, the terms may be changed depending on the intention or convention of those skilled in the art or the introduction of new technology. Some terms have been arbitrarily selected by the applicant and their meanings are explained in detail in the following description as needed. Thus, the definitions of the terms used in the invention should be determined based on the whole content of this specification together with the intended meanings of the terms rather than their simple names or meanings.

[44] The invention performs precoding on data before transmitting the data through an antenna to obtain a coding gain so that the data is robust to frequency selective fading and is also not affected by channels in various channel environments.

[45] FIG. 1 illustrates an example method in which input data is precoded to spread the input data. Specifically, input data values are precoded so that they are spread and transmitted over multiple subcarriers. This reduces the probability of loss of a data value carried in a specific subcarrier when the transmitted data is decoded at the receiving end. For example, a precoder which performs precoding can spread data values in the frequency domain such that a data value for allocation to each subcarrier is allocated to at least two subcarriers. This can increase overall data transmission efficiency. [46] FIG. 1 illustrates an example precoding scheme that can be referred to as a

Vandermonde matrix. A plurality of data (data elements or data values) for transmission can be arranged in the same number (L) of parallel rows as the number of subcarriers. For example, θ can be represented by the following Mathematical Expression 1 and can also be defined in a different manner. Elements of the Vandermonde matrix can be controlled using Mathematical Expression 1. Controlling the elements of the Vandermonde matrix can spread each input value over at least two values according to their characteristics.

[47] MATHEMATICAL EXPRESSION 1

[48]

[49] In Mathematical Expression 1, L denotes the number of subcarriers. When x is a data group that is input for precoding and y is a data group into which the input data group is precoded according to a matrix illustrated in FIG. 1, y can be expressed by Mathematical Expression 2 as follows.

[50] MATHEMATICAL EXPRESSION 2

[51] y — ksx

[52] FIG. 2 is a block diagram illustrating a detailed embodiment of a signal transmitter

(or an apparatus for transmitting signals) including a single transmit antenna according to the invention in an example where the precoding scheme illustrated in FIG. 1 is applied. The example of FIG. 2 illustrates how a signal is transmitted using an OFDM scheme when video data such as a broadcast signal is transmitted. For example, the signal transmitter of FIG. 2 may be a broadcast signal transmitter according to a Digital Video Broadcasting (DVB) system.

[53] The embodiment of FIG. 2 may include an outer coder 201, an outer interleaver

202, an inner coder 203, an inner interleaver 204, a symbol mapper 205, a precoder 206, a frame builder 207, a modulator 208, and a transmission unit 209.

[54] The outer coder 201 and the outer interleaver 202 can encode and interleave multiplexed data in order to increase transmission performance of the multiplexed data, respectively. Here, for example, Reed-Solomon coding can be used as a method for outer coding and convolution interleaving can be used as a method for interleaving. [55] The inner coder 203 and the inner interleaver 204 reencode and reinterleave the signal for transmission to deal with errors that may occur in the transmitted signal, respectively. The inner coder 203 can encode the signal for transmission (also referred to as "transmission signal") according to a punctured convolution code. For example, in the case of DVB-T, the inner interleaver 204 may use a native or in-depth interleaving scheme according to the usage or management of memory in transmission modes of 2k, 4k, and 8k.

[56] The symbol mapper 205 can map the transmission signal to a symbol according to a scheme such as 16QAM, 64QAM, or QPSK taking into consideration a transmission parameter signal and a pilot signal according to the transmission mode. The precoder 206 codes input symbols by spreading them over carriers so as to be robust to frequency selective fading of channels. For example, the precoder 206 can spread input symbol values over multiple subcarriers using the precoding method of FIG. 1. Accordingly, even if fading has occurred in a specific frequency band in frequency selective fading channels, the influence of the fading can be reduced since subcarriers in the frequency band have spread values.

[57] The frame builder 207 converts a precoded symbol into the time domain and inserts a guard interval into a data section of the time-domain symbol to generate an OFDM symbol and cumulates such generated OFDM symbols to create a frame. For example, when employing DVB Terrestrial (DVB-T), each frame includes 68 OFDM symbols. Each OFDM symbol includes 6817 carriers in an 8k mode and 1705 carriers in a 2k mode. The frame also includes a distributed training signal, a continuous training signal, and a Transmission Parameter Signal (TPS) carrier. The TPS includes all information of transmission parameters such as the length of a guard interval and the number of carriers of each OFDM symbol that is currently transmitted.

[58] The modulator 208 modulates a plurality of OFDM data in the frame output from the frame builder 207 into a format that can be carried on subcarriers.

[59] The transmission unit 209 converts each subcarrier from the modulator 208 into an analog signal and transmits the analog signal after upconversion into an RF signal.

[60] The precoder 206 may be included in the frame builder 207 although the precoder

206 is illustrated as being separated from the frame builder 207 in FIG. 2 for ease of explanation.

[61] FIG. 3 illustrates detailed examples of the precoder 206, the frame builder 207, the modulator 208, and the transmission unit 209 in FIG. 2. A signal arranger 301 and a precoding unit 203 in FIG. 3 correspond to the precoder 206 in FIG. 2 and a signal converter 303, a second signal arranger 304, and a guard interval inserter 305 in FIG. 3 correspond to the frame builder 207 in FIG. 2. In another example, the signal arranger 301, the precoding unit 302, the signal converter 303, the second signal arranger 304, and the guard interval inserter 305 in FIG. 3 may be considered a frame builder.

[62] That is, the first signal arranger 301 arranges a plurality of sequentially input data

(data elements) for processing the data elements in parallel on a specific unit basis. For example, the first signal arranger 301 may arrange data using a serial/parallel converter that converts serial input data into parallel data. The precoding unit 302 codes a plurality of parallel data elements output from the first signal arranger 301 by spreading them over carriers so as to be robust to frequency selective fading of channels. That is, the precoding unit 302 can spread input symbol values over multiple subcarriers. Accordingly, even if fading has occurred in a specific frequency band in frequency selective fading channels, the influence of the fading can be reduced since subcarriers in the frequency band have spread values. In addition, controlling the coding scheme of the precoding unit 302 can reduce peak-to-average -power ratio (PAPR) of the signal converter 303.

[63] The signal converter 303 converts a plurality of data (data elements or values) output from the precoding unit 302 into the time domain. The signal converter 303 can convert input data into the time domain according to an inverse Fourier transform algorithm. The signal converter 303 can use an Inverse Discrete Fourier Transform (IDFT) or Inverse Fast Fourier Transform (IFFT) algorithm to convert input data into the time domain.

[64] The second signal arranger 304 serially arranges and outputs a plurality of time- domain data output from the signal converter 303. For example, the second signal arranger 304 can arrange data using a parallel/serial converter that converts a plurality of parallel input data into serial data.

[65] The guard interval inserter 305 inserts guard intervals into signals modulated according to the procedure described above and outputs the resulting signals. For example, the guard interval inserter 305 may add specific sections in a plurality of data output from the second signal arranger 304, as guard intervals, to the plurality of data.

[66] In the case of DVB-T, the inserted guard interval is a cyclic continuation including a copy of data in the data section and varies in length depending on the transmission mode. The guard interval can prevent a reduction in system performance due to Inter- Symbol Interference (ISI) and ghost.

[67] FIG. 4 is a block diagram illustrating a detailed embodiment of a signal receiver (or an apparatus for receiving signals) including a single antenna according to the invention, which can predecode data that was precoded and transmitted by the transmitter. The embodiment of FIG. 4 can be included in a DVB receiver.

[68] The embodiment of the signal receiver according to the invention shown in FIG. 4 may include a reception unit 401, a synchronizer 402, a demodulator 403, a frame parser 404, a precoding decoder 405, a symbol demapper 406, an inner decoder 408, an outer deinterleaver 409, and an outer decoder 410.

[69] The reception unit 401 do wncon verts a frequency band of a received RF signal and converts it into a digital signal. The synchronizer 402 achieves frequency and time- domain synchronization of the received signal and outputs the synchronized signal. The synchronizer 402 can use an offset in the frequency domain of the data output from the demodulator 403 in order to achieve synchronization of the frequency domain signal.

[70] The demodulator 403 demodulates the received data by performing the reverse of the process of the modulator 208 in the transmitter.

[71] The frame parser 404 performs FFT on the demodulated signal for conversion into the frequency domain and parses data (i.e., valid data) in a data section of the frequency domain signal, excluding a guard interval that is included in the signal according to the frame structure of the signal, and outputs the parsed data to the precoding decoder 405.

[72] The precoding decoder 405 decodes data values spread over subcarriers of the data output from the frame parser 404 into respective values that were allocated to the subcarriers. That is, the precoding decoder 405 despreads data values, each being spread over two or more subcarriers, into values that were allocated to the subcarriers before spreading. To accomplish this, the precoding decoder 405 may calculate and output input data using an inverse matrix illustrated in FIG. 1.

[73] The symbol demapper 406 reconstructs the predecoded data into a sequence of bits.

The inner deinterleaver 407 performs deinterleaving, which is the reverse of interleaving, on the data bit sequence that was interleaved at the transmitter. The inner decoder 408 decodes the deinterleaved data to correct errors contained in the data. The outer deinterleaver 409 and the outer decoder 410 again perform a deinterleaving process and an error-correction decoding process on the data output from the inner decoder 408, respectively.

[74] The precoding decoder 405 in the example of FIG. 4 performs decoding on the precoded signal, thereby preventing information elements carried on some subcarriers from being totally lost by a frequency selective fading channel during communication.

[75] FIG. 5 illustrates an embodiment of a method for transmitting and receiving signals according to the invention. The embodiment of a method for transmitting and receiving signals according to the invention will now be described with reference to FIG. 5.

[76] First, precoding is performed by spreading data over the frequency domain such that a data value for allocation to each subcarrier in the frequency domain is allocated to two or more subcarriers (S501).

[77] The precoded data values are converted into the time-domain (S502). The time- domain data values are converted into an RF-band signal to be transmitted (S503). [78] When the RF-band signal modulated in the above manner is received, the received signal is converted into a digital signal (S504). The signal in the time domain is then converted into a signal in the frequency domain (S505). This conversion into the frequency domain is performed taking into consideration synchronization of signals in the time domain.

[79] Data values of subcarriers in the frequency domain are results of spreading of each of data values, which were allocated to the subcarriers, over two or more subcarriers. That is, data of a subcarrier includes data values spread according to the precoding calculation of S501 in the frequency domain. Therefore, the reverse calculation of the precoding of the above step S501 is performed to obtain a plurality of original data in the frequency domain (S506).

[80] Accordingly, even if data in the frequency domain is partially lost due to frequency selective fading of a transport channel, it is possible to obtain data little affected by the frequency selective fading by performing the reverse process of the spreading process since the data values of subcarriers in the frequency domain are spread versions of original data values in the frequency domain.

[81] The MIMO technology is divided into a spatial multiplexing scheme and a spatial diversity scheme. According to the spatial multiplexing, the transmitter and receiver use multiple antennas to simultaneously transmit different data, thereby increasing the data transfer rate without increasing system bandwidth. According to the spatial diversity, data of the same information is transmitted through multiple transmit antennas to obtain transmission diversity.

[82] FIG. 6 schematically illustrates a transceiver system where precoding is applied in the spatial multiplexing scheme according to an embodiment of the invention. The transceiver system uses MIMO for multiple inputs/outputs. For ease of the following explanation, let us assume that the transmitter and receiver use two transmit and receive antennas, respectively.

[83] The transceiver system includes a precoding unit 600, a first transmit antenna 610, a second transmit antenna 620, a first receive antenna 630, a second transmit antenna 640, and a decoding unit 650.

[84] The precoding unit 600, the first transmit antenna 610, and the second transmit antenna 620 are components of the transmitter and the first receive antenna 630, the second transmit antenna 640, and the decoding unit 650 are components of the receiver.

[85] The first transmit antenna 610, the second transmit antenna 620, the first receive antenna 630, and the second receive antenna 640 can transmit or receive signals according to a dual polarization diversity scheme. This scheme can reduce inter- channel correlation using vertical polarity and horizontal polarity of transmission signals.

[86] When the spatial multiplexing scheme is applied in the case of FIG. 6, the first transmit antenna 610 and the second transmit antenna 620 transmit different data.

[87] The preceding unit 600 achieves a coding gain through precoding before transmitting input symbol data to the antennas. The precoding unit 600 can use a full- rate full-diversity code designed to obtain improved reception performance, regardless of transport channel characteristics.

[88] FIG. 7 illustrates a code for precoding in the spatial multiplexing scheme according to an embodiment of the invention. The code of FIG. 7 is one of a variety of codes for obtaining a coding gain. In FIG. 7, "C" denotes a code matrix of a golden code.

[89] In FIG. 7, xl, x2, x3, and x4 denote symbol data input to the precoding unit 600.

The characteristics of a code matrix are determined by constants in the code matrix, which are shown in FIG. 7.

[90] If symbol data elements xl, x2, x3, and x4 are input to the precoding unit 600, the precoding unit 600 precodes the symbol data elements to a code matrix as shown in FIG. 7. The precoded data elements are transmitted using the first transmit antenna 610 and the second transmit antenna 620.

[91] When a row of the matrix represents a transmission time at which data is transmitted, a column can represent an antenna through which the data is transmitted. When a row of the matrix represents an antenna through which data is transmitted, a column can represent a transmission time at which the data is transmitted.

[92] Specifically, when the first row represents data transmitted at time "t" and the second row represents data transmitted at time "t+T", the first column can represent data transmitted through the first transmit antenna 610 and the second column can represent data transmitted through the second transmit antenna 620. When the first column represents data transmitted through the second transmit antenna 620, the second column represents data transmitted through the first transmit antenna 610.

[93] Alternatively, when the first column represents data transmitted at time "t" and the second column represents data transmitted at time "t+T", the first row can represent data transmitted through the first transmit antenna 610 and the second row can represent data transmitted through the second transmit antenna 620. When the first row represents data transmitted through the second transmit antenna 620, the second row represents data transmitted through the first transmit antenna 610.

[94] For example, if the first row of the matrix represents data transmitted at time "t", the second row represents data transmitted at time "t+T". In addition, if the first column of the matrix represents data transmitted through the first transmit antenna 610, the second column represents data transmitted through the second transmit antenna 620. [95] That is, when the first transmit antenna 610 transmits data of the first row and the first column at time "t", the second transmit antenna 620 transmits data of the first row and the second column. In addition, when the first transmit antenna 610 transmits data of the second row and the first column at time "t+T", the second transmit antenna 620 transmits data of the second row and the second column.

[96] The first transmit antenna 610 and the second transmit antenna 620 can transmit signals according to a dual polarization diversity scheme.

[97] For example, when the first transmit antenna 610 uses a polarization antenna inclined at -45° and the second transmit antenna 620 uses a polarization antenna inclined at 45°, signals transmitted through the transmit antennas are orthogonal to each other. Here, the first receive antenna 630 uses a polarization antenna inclined at - 45° and the second receive antenna 640 uses a polarization antenna inclined at 45°. The inclined angles of the polarization antenna are purely illustrative and the present invention is not limited to these angle values.

[98] The first receive antenna 630 and the second receive antenna 640 of the receiver receive signals that have undergone channels after being transmitted from the transmitter. The decoding unit 650 decodes the received signals to reconstruct symbol data as before precoding. Specifically, the decoding unit 650 decodes received data using a Maximum Likelihood (ML) scheme and performs de-matrixing on the data using the reverse of the golden code to reconstruct symbols as before precoding.

[99] FIG. 8 schematically illustrates a transceiver system where precoding is applied in the spatial diversity scheme according to an embodiment of the invention. The transceiver system uses MIMO for multiple inputs/outputs. For ease of the following explanation, let us assume that the transmitter and receiver use two transmit and receive antennas, respectively.

[100] The transceiver system includes a precoding unit 800, a third transmit antenna 810, a fourth transmit antenna 820, a third receive antenna 830, a fourth receive antenna 840, and a decoding unit 850.

[101] The precoding unit 800, the third transmit antenna 810, and the fourth transmit antenna 820 are components of the transmitter and the third receive antenna 830, the fourth receive antenna 840, and the decoding unit 850 are components of the receiver.

[102] The third transmit antenna 810, the fourth transmit antenna 820, the third receive antenna 830, and the fourth receive antenna 840 can transmit or receive signals according to a dual polarization diversity scheme.

[103] When the spatial diversity scheme is applied in the case of FIG. 8, the third transmit antenna 810 and the fourth transmit antenna 820 transmit data of the same information.

[104] The precoding unit 800 achieves a coding gain through precoding before transmitting input symbol data to the antennas. The precoding unit 800 can use a Space Time Block Code (STBC), a Space Time Trellis Code (STTC), or the like to allow transmitted data to be robust to channel environments.

[105] FIG. 9 illustrates a code for precoding in a spatial diversity scheme according to an embodiment of the invention. FIG. 9 illustrates a 4-state Quadrature Phase Shift Keying (OPSK) STTC which is one of a variety of codes for obtaining a coding gain.

[106] A left circle in FIG. 9 illustrates a 4-state QPSK constellation and a right diagram is a 4-state transition diagram. The constellation shows four states of 0 to 3 and the diagram shows each state and data that is transmitted when each state is transitioned.

[107] The precoding unit 800 transmits data according to input data and the current state using the constellation and the state transition diagram.

[108] For example, let us assume that the initial state is "0" and data elements "0 1 2 3 2

2" are sequentially input to the precoding unit 800. Since data input at the current state "0" is "0", the next state is "0". Since the state "0" has been transitioned to "0", the precoding unit 800 outputs "00". One antenna transmits one data element.

[109] In the above embodiment, the positions of transmitted data and the antennas are not fixed. The third transmit antenna 810 may transmit the front of the two output data and may also transmit the rear. When it is assumed that the third transmit antenna 810 transmits the rear data and the fourth transmit antenna 820 transmits the front data, the third transmit antenna 810 and the fourth transmit antenna 820 transmit "0" and "0", respectively.

[110] Since data input at the changed current state "0" is "1", the next state is "1". Since the state "0" has been transitioned to "1", the precoding unit 800 outputs "10". Accordingly, the third transmit antenna 810 and the fourth transmit antenna 820 transmit "0" and "1", respectively.

[I l l] Since the changed current state is "1" and the next input bit is "2", the next state is

"2". Since the state "1" has been transitioned to "2", the precoding unit 800 outputs "21". Accordingly, the third transmit antenna 810 and the fourth transmit antenna 820 transmit "1" and "2", respectively.

[ 112] According to the above procedure, the third transmit antenna 810 sequentially transmits data "0 0 1 2 3 2" and the fourth transmit antenna 820 sequentially transmits data "0 1 2 3 2 2".

[113] The third transmit antenna 810 and the fourth transmit antenna 820 can transmit signals according to a dual polarization diversity scheme. For example, when the third transmit antenna 810 uses a polarization antenna inclined at -45° and the fourth transmit antenna 820 uses a polarization antenna inclined at 45°, signals transmitted through the transmit antennas are orthogonal to each other. Here, the third receive antenna 630 uses a polarization antenna inclined at -45° and the fourth receive antenna 640 uses a polarization antenna inclined at 45°. The inclined angles of the polarization antenna are purely illustrative and the present invention is not limited to these angle values.

[114] The first receive antenna 630 and the second receive antenna 640 of the receiver receive signals that have undergone channels after being transmitted from the transmitter. The decoding unit 850 decodes the received data values according to a Maximum Likelihood (ML) scheme to reconstruct the transmitted data.

[115] In the case where the dual polarization diversity scheme is used to perform the precoding process for obtaining a coding gain as described above, it is possible to increase reception performance not only in LOS channel environments but also in channel environments such as Rayleigh fading that are generally favorable for the MIMO system.

[116] FIG. 10 is a block diagram illustrating another embodiment of a signal transmitter using precoding according to the invention. The signal transmitter of FIG. 10 may be a signal transmission system that transmits video data such as broadcast signals. For example, the signal transmitter of FIG. 10 may be a signal transmitter according to a Digital Video Broadcasting (DVB) system. This embodiment of the signal transmission system according to the invention will now be described with reference to FIG. 10.

[117] The embodiment of FIG. 10 may include an outer coder 1000, an outer interleaver

1010, an inner coder 1020, an inner interleaver 1030, a symbol mapper 1040, a MIMO precoder 1050, a frame builder 1060, a modulator 1070, and a transmission unit 1080. The embodiment of FIG. 10 is described below focusing on how signals are processed in the signal transmission system.

[118] The outer coder 1000 and the outer interleaver 1010 can encode and interleave multiplexed data in order to increase transmission performance of the multiplexed data, respectively. Here, for example, Reed-Solomon coding can be used as a method for outer coding and convolution interleaving can be used as a method for interleaving.

[119] The inner coder 1020 and the inner interleaver 1030 reencode and reinterleave the signal for transmission to deal with errors that may occur in the transmitted signal, respectively. The inner coder 1020 can encode the signal for transmission (also referred to as "transmission signal") according to a punctured convolution code. For example, in the case of DVB-T, the inner interleaver 1030 may use a native or in-depth interleaving scheme according to the usage or management of memory in transmission modes of 2k, 4k, and 8k.

[120] The symbol mapper 1040 can map the transmission signal to a symbol according to a scheme such as 16QAM, 64QAM, or QPSK taking into consideration a transmission parameter signal and a pilot signal according to the transmission mode.

[121] The MIMO precoder 1050 precodes symbols mapped at the symbol mapper 1040 so that they are carried on multiple transmit antennas. The MIMO precoder 1050 can obtain a coding gain through this precoding.

[122] The MIMO precoder 1050 can use the golden code as shown in FIG. 7 or the like as an example for precoding for spatial multiplexing. The MIMO precoder 1050 can use a Space Time Block Code (STBC), a Space Time Trellis Code (STTC), or the like as an example for precoding for spatial diversity. These codes have been described above.

[123] The frame builder 1060 converts a precoded symbol into the time domain through

IFFT and inserts a guard interval into a data section of the time-domain symbol to generate an OFDM symbol and cumulates such generated OFDM symbols to create a frame.

[124] For example, when employing DVB Terrestrial (DVB-T), each frame includes 68

OFDM symbols. Each OFDM symbol includes 6817 carriers in an 8k mode and 1705 carriers in a 2k mode. The frame also includes a distributed training signal, a continuous training signal, and a Transmission Parameter Signal (TPS) carrier. The TPS includes all information of transmission parameters such as the length of a guard interval and the number of carriers of each OFDM symbol that is currently transmitted.

[125] The modulator 1070 modulates a plurality of OFDM data in the frame output from the frame builder 1060 into a format that can be carried on subcarriers.

[126] The transmission unit 1080 converts each subcarrier from the modulator 1070 into an analog signal and transmits the analog signal through a dual polarization antenna after upconversion into an RF signal according to a dual polarization diversity scheme.

[127] FIG. 11 is a block diagram schematically illustrating another embodiment of a signal receiver using precoding according to the invention in the case where multiple receive paths are provided. The embodiment of FIG. 11 can be included in a DVB receiver. This embodiment can receive and predecode a broadcast signal that was precoded and transmitted by the transmitter or FIG. 10.

[128] The embodiment according to the invention shown in FIG. 11 includes a reception unit 1100, a synchronizer 1110, a demodulator 1120, a frame parser 1130, a MIMO precoding decoder 1140, a symbol demapper 1150, an inner decoder 1170, an outer deinterleaver 1180, and an outer decoder 1190.

[129] The reception unit 1100 receives an RF signal that was transmitted according to a dual polarization diversity scheme and downconverts a frequency band of the RF signal and then converts it into a digital signal. The synchronizer 1110 achieves frequency and time-domain synchronization of the received signal output from the reception unit 1100 and outputs the synchronized signal. The synchronizer 1110 can use an offset in the frequency domain of the data output from the demodulator 1120 in order to achieve synchronization of the frequency domain signal.

[130] The demodulator 1120 demodulates the received data output from the synchronizer 1110 by performing the reverse of the process of the modulator 208 in the transmitter.

[131] The frame parser 1130 performs FFT on the demodulated signal for conversion into the frequency domain and parses data (i.e., valid symbol data) in a data section of the frequency domain signal, excluding a guard interval that is included in the signal according to the frame structure of the signal, and outputs the parsed data to the MIMO precoding decoder 1140.

[132] The MIMO precoding decoder 1140 decodes symbol data output from the frame parser 1130 according to the reverse of the precoding scheme of the transmitter and outputs a data sequence. For example, the MIMO precoding decoder 1140 decodes the symbol data according to a scheme corresponding to the precoding scheme, in which the MIMO precoder 1050 of FIG. 10 precodes symbols so as to be carried on multiple transmit antennas, and outputs a single data sequence. The symbol demapper 1150 can reconstruct the decoded symbol data of each subcarrier output from the MIMO precoding decoder 1140 into a bit sequence.

[133] The inner deinterleaver 1160 performs deinterleaving, which is the reverse of interleaving, on an interleaved data sequence. The inner decoder 1170 decodes the dein- terleaved data to correct errors contained in the data. The outer deinterleaver 1180 and the outer decoder 1190 again perform a deinterleaving process and an error-correction decoding process on the data output from the inner decoder 1170, respectively.

[134] FIG. 12 is a block diagram illustrating another embodiment of a signal transmitter using precoding according to the invention in the case where multiple transmission paths are provided. The following description will be given with reference to an example where two transmission paths are provided for ease of explanation.

[135] The embodiment of FIG. 12 includes an outer coder 1200, an outer interleaver

1210, an inner coder 1220, an inner interleaver 1230, a symbol mapper 1240, a MIMO precoder 1250, a first frame builder 1260, a second frame builder 1265, a first modulator 1270, a second modulator 1275, a first transmission unit 1280, and a second transmission unit 1285.

[136] A detailed description of signal processing processes of the components 1200 to

1250 in FIG. 12 is omitted here since they are similar to those described above with reference to FIG. 10.

[137] The MIMO precoder 1250 precodes symbols mapped at the symbol mapper 1240 so that they are carried on multiple transmit antennas. For example, when two transmission paths are provided, the MIMO precoder 1250 outputs the precoded data to the first frame builder 1260 or the second frame builder 1265.

[138] When the spatial diversity scheme is applied, the MIMO precoder 1250 outputs data of the same information to the first frame builder 1260 and the second frame builder 1265. When the spatial multiplexing scheme is applied, the MIMO precoder 1250 outputs different data to the first frame builder 1260 and the second frame builder 1265.

[139] Each of the first frame builder 1260 and the second frame builder 1265 receives and converts a precoded symbol into the time domain through IFFT and inserts a guard interval into a data section of the time-domain symbol to generate an OFDM symbol and cumulates such generated OFDM symbols to create a frame.

[140] For example, when employing DVB Terrestrial (DVB-T), each frame includes 68

[141] The first and second modulators 1270 and 1275 modulate a plurality of OFDM data in the frames output from the first and second frame builders 1260 and 1265 into a format that can be carried on subcarriers, respectively.

[142] The first and second transmission units 1280 and 1285 convert subcarriers from the first and second modulators 1270 and 1275 into analog signals and transmit the analog signals through dual polarization antennas after upconversion into RF signals according to a dual polarization diversity scheme.

[143] FIG. 13 is a block diagram schematically illustrating another embodiment of a signal receiver using precoding according to the invention in the case where multiple receive paths are provided. The embodiment of FIG. 13 can be included in a DVB receiver. This embodiment can receive and predecode a broadcast signal that was precoded and transmitted by the transmitter of FIG. 12.

[144] The following description will be given with reference to an example where two receive paths are provided for ease of explanation.

[145] The signal receiver of FIG. 13 includes a first reception unit 1300, a second reception unit 1305, a first synchronizer 1310, a second synchronizer 1315, a first demodulator 1320, a second demodulator 1325, a first frame parser 1330, a second frame parser 1335, a MIMO precoding decoder 1340, a symbol demapper 1350, an inner decoder 1370, an outer deinterleaver 1380, and an outer decoder 1390.

[146] Each of the first and second reception units 1300 and 1305 receives an RF signal that was transmitted according to a dual polarization diversity scheme and downconverts a frequency band of the RF signal and then converts it into a digital signal. The first and second synchronizers 1310 and 1315 achieve frequency and time- domain synchronization of received signals output from the first and second reception units 1300 and 1305 and output the synchronized signals. The first and second synchronizers 1310 and 1315 can use an offset in the frequency domain of the data output from the first and second demodulators 1320 and 1325 in order to achieve synchronization of the frequency domain signal.

[147] The first demodulator 1320 demodulates received data output from the first synchronizer 1310 by performing the reverse of the process of the first modulator 1270 in the transmitter. The second demodulator 1325 demodulates received data output from the second synchronizer 1315 by performing the reverse of the process of the second modulator 1275 in the transmitter.

[148] The first frame parser 1330 performs FFT on a signal demodulated at the first demodulator 1320 for conversion into the frequency domain and parses data (i.e., valid symbol data) in a data section of the frequency domain signal, excluding a guard interval that is included in the signal according to the frame structure of the signal, and outputs the parsed data to the MIMO precoding decoder 1340. Likewise, the second frame parser 1335 performs FFT on a signal demodulated at the second demodulator 1320 for conversion into the frequency domain and parses data (i.e., valid symbol data) in a data section of the frequency domain signal, excluding a guard interval that is included in the signal according to the frame structure of the signal, and outputs the parsed data to the MIMO precoding decoder 1340.

[149] The MIMO precoding decoder 1340 decodes symbol data output from the first and second frame parsers 1330 and 1335 according to the reverse of the precoding scheme of the transmitter and outputs a data sequence.

[150] For example, the MIMO precoding decoder 1340 decodes the symbol data according to a scheme corresponding to the precoding scheme, in which the MIMO precoder 1250 of FIG. 12 precodes symbols so as to be carried on multiple transmit antennas, and outputs a single data sequence to the inner deinterleaver 1360. The symbol demapper 1350 can reconstruct the decoded symbol data of each subcarrier output from the MIMO precoding decoder 1340 into a bit sequence.

[151] A detailed description of signal processing processes of the components 1360 to

1390 in FIG. 13 is omitted here since they are similar to those described above with reference to FIG. 11.

[152] FIG. 14 is a flow chart illustrating a method for transmitting and receiving signals using precoding according to another embodiment of the invention.

[153] First, data to be transmitted is MIMO-precoded for transmission through multiple antennas (S 1401). Through the precoding, it is possible to obtain a coding gain. The number of the antennas may be equal to the number of possible data transmission paths.

[154] The precoded data is modulated at multiple modulators (S 1402) and the modulated data are converted into analog signals at multiple transmission units according to a dual polarization scheme (S 1403). [155] Each of the analog signals produced through conversion at step S1403 is transmitted through a separate dual polarization antenna (S 1404). When the spatial diversity scheme is applied, data of the same information is transmitted through each path, and therefore the transmission units transmit data of the same information. On the other hand, when the spatial multiplexing scheme is applied, different data is transmitted through each path, and therefore the transmission units transmit different data.

[156] The reception units receive the transmitted signals through multiple receive antennas and convert them into digital signals (S 1405). The digital signals are demodulated into digital data (S 1406).

[157] The demodulated data are decoded according to a scheme corresponding to the precoding scheme applied at step S 1401 to obtain a data sequence (S 1407).

[158] It will be easy for those skilled in the art to modify or change the present invention from this specification. Thus, although the embodiments of the invention have been clearly described, various modifications of the embodiments can be made without departing from the spirit or scope of the invention and should be construed as being included in the spirit or scope of the invention.

Claims

[1] An apparatus for transmitting signals, the apparatus comprising: a precoder for precoding input data; a frame builder for converting data output from the precoder into a time domain, inserting a guard interval into a valid data section converted into the time domain to generate a transmission symbol, and cumulating transmission symbols to create a frame; a modulator for modulating data of the frame; and a transmission unit for converting the modulated data into analog data and transmitting the analog data.

[2] The apparatus according to claim 1, wherein the precoder includes: a first signal arranger for arranging serially input data elements in parallel rows of data elements in equal number to a number of subcarriers; and a precoding unit for multiplying the arranged data elements by a Vandermonde matrix and outputting the multiplied data elements.

[3] The apparatus according to claim 2, wherein the frame builder includes: a signal converter for converting the precoded data into time-domain data; a second signal arranger for serially arranging data output in parallel from the signal converter and outputting the serially arranged data; and a guard interval inserter for inserting a guard interval into a valid data section including the data output from the second signal arranger.

[4] The apparatus according to claim 1 , wherein the precoder precodes the input data so that the input data can be transmitted in a multiplexed manner.

[5] The apparatus according to claim 1, wherein the precoder precodes and outputs the input data to multiple paths.

[6] The apparatus according to claim 5, wherein the frame builder includes the same number of parallel frame builders as the number of the multiple paths, the modulator includes the same number of parallel modulators as the number of the multiple paths, and the transmission unit includes the same number of parallel transmission units as the number of the multiple paths.

[7] The apparatus according to claim 1, wherein the precoder precodes the input data using a golden code when a spatial multiplexing scheme is used as a Multi-Input Multi-Output (MIMO) scheme.

[8] The apparatus according to claim 1, wherein the precoder precodes the input data using a Space Time Trellis Code (STTC) when a spatial diversity scheme is used as a MIMO scheme.

[9] The apparatus according to claim 1 , wherein the transmission unit converts the modulated data into analog data according to a dual polarization diversity scheme and transmits the analog data.

[10] A method for transmitting signals, the method comprising: precoding input data; converting the precoded data into a time domain, inserting a guard interval into a valid data section converted into the time domain to generate a modulation symbol, and cumulating modulation symbols to create a frame; modulating data of the created frame; and converting the modulated data into analog data and transmitting the analog data.

[11] The method according to claim 10, wherein the precoding step includes multiplying the input data by a Vandermonde matrix and outputting the multiplied data elements.

[12] The method according to claim 10, wherein the precoding step includes precoding the input data so that the input data can be transmitted in a multiplexed manner.

[13] The method according to claim 10, wherein the precoding step includes precoding and outputting the input data to multiple paths, wherein the precoded data undergoes framing, modulating, and transmitting processes in each of the paths.

[14] The method according to claim 10, wherein the precoding step includes precoding the input data using a golden code when a spatial multiplexing scheme is used as a Multi- Input Multi-Output (MIMO) scheme.

[15] The method according to claim 10, wherein the precoding step includes precoding the input data using a Space Time Trellis Code (STTC) when a spatial diversity scheme is used as a MEVlO scheme.

[16] The method according to claim 10, wherein the transmitting step includes converting the modulated data into analog data according to a dual polarization diversity scheme and transmitting the analog data.

[17] An apparatus for receiving signals, the apparatus comprising: a reception unit for converting received analog data into digital data; a synchronizer for restoring synchronization of the digital data; a demodulator for demodulating the data whose synchronization has been restored; a frame parser for parsing the demodulated data in a frequency domain and outputting symbol data in a valid data section; and a precoding decoder for decoding the symbol data according to reverse precoding and outputting a symbol data sequence.

[18] The apparatus according to claim 17, wherein the reception unit converts received analog data into digital data according to a dual polarization diversity scheme.

[19] The apparatus according to claim 17, wherein the reception unit includes the same number of parallel reception units as the number of multiple paths through which data was precoded and transmitted by a transmitting apparatus, the synchronizer includes the same number of parallel synchronizers as the number of the multiple paths, the demodulator includes the same number of parallel demodulators as the number of the multiple paths, and the frame parser includes the same number of parallel frame parsers as the number of the multiple paths.

[20] The apparatus according to claim 17, wherein, when a spatial multiplexing scheme is used as a Multi-Input Multi-Output (MIMO) scheme, the precoding decoder decodes received data according to a Maximum Likelihood (ML) method and performs de-matrixing on the decoded data according to a reverse golden code to reconstruct symbol data as before precoding.

[21] The apparatus according to claim 17, wherein, when a spatial diversity scheme is used as a MIMO scheme, the precoding decoder decodes received data in a Maximum Likelihood (ML) method to reconstruct symbol data as before precoding.

[22] The apparatus according to claim 17, wherein the precoding decoder receives symbol data elements output from the frame parser and performs calculations for despreading the symbol data elements into respective symbol data elements of subcarriers.

[23] A method for receiving signals, the method comprising: converting received analog data into digital data; restoring synchronization of the digital data; demodulating the data whose synchronization has been restored; parsing the demodulated data in a frequency domain and outputting symbol data in a valid data section; and decoding the symbol data according to reverse precoding and outputting a symbol data sequence.

[24] The method according to claim 23, wherein the receiving step includes converting received analog data into digital data according to a dual polarization diversity scheme.

[25] The method according to claim 23, wherein each of the restoring, demodulating, and parsing steps is performed the same number of times as the number of multiple paths through which data was precoded and transmitted by a transmitting apparatus.

[26] The method according to claim 23, wherein, when a spatial multiplexing scheme is used as a Multi- Input Multi-Output (MIMO) scheme, the decoding step includes decoding received data according to a Maximum Likelihood (ML) met hod and performing de-matrixing on the decoded data according to a reverse golden code to reconstruct symbol data as before precoding.

[27] The method according to claim 23, wherein, when a spatial diversity scheme is used as a MIMO scheme, the decoding step includes decoding received data in a Maximum Likelihood (ML) method to reconstruct symbol data as before precoding.

[28] The method according to claim 23, wherein the decoding step includes performing calculations for despreading symbol data elements output through the parsing into respective symbol data elements of subcarriers.