KR20120070083A - Orthogonal frequency division multiplexing system that is based on ciod(coordinate interleaved orthogonal design) and dsfbc(double space-frequency block codes) - Google Patents

Abstract

PURPOSE: An orthogonal frequency division multiplexing(OFDM) system and a method for the same based on a coordinate interleaved orthogonal design(CIOD) and a double space frequency block code(DSFBC) are provided to secure full-rate full-diversity by effectively draw transmission diversity if the number of transmitting antennas are more than the number of receiving antennas. CONSTITUTION: A modulating part(101) modulates an input data stream. A de-multiplexing part(102) divides the modulated data stream into two streams. A delaying part(103) delays two streams according to modes and outputs the delayed streams. Two encoders(104, 105) receive the streams from the delaying part and encodes the streams. A constellation-rotating part(106) constellation-rotates the encoded signals according to the modes. An inverse fast Fourier transforming parts(107 to 110) converts the constellation-rotated encoded signals into signals on a time axis to be output.

Description

OPDM system and method thereof based on CIOD and DSFBC {Orthogonal frequency division multiplexing system that is based on CIOD (coordinate interleaved orthogonal design) and DSFBC (double space-frequency block codes)

The present invention relates to an OFDM system based on space-frequency block codes (SFBC) from coordinate interleaved orthogonal design (CIOD), which can be classified as multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) technology.

In the conventional method, it is common to increase transmission diversity using STBC based on two transmission antennas. When four transmission antennas are used, it is intended to increase transmission diversity with four transmission antennas mainly using QSTBC. Since QSTBC basically does not bring full-diversity performance, a special constellation rotation is needed at the transmitter, and accordingly, the receiver can obtain full-diversity (ie, diversit order 4) through complex decoding methods. Also, in general, STBC is applied in OFDM symbol units to apply QSTBC like OFDM.

An embodiment of the present invention provides an OFDM system and method thereof based on CIOD and DSFBC.

In the embodiment of the present invention, when obtaining two or more transmission full-diversity, the OFDM of the complexity of the transmitter and the receiver can be obtained with linear complexity while also doubling the full-diversity performance and transmission rate by half with low complexity. A system and method are provided.

In the embodiment of the present invention, when obtaining two or more transmission full-diversity, while obtaining the complexity of the transceiver in linear complexity, while still having low complexity and doubling the half full-diversity performance and transmission rate,

Provided are an OFDM system having a complexity that can be implemented by applying space-frequency block coding of SFBC, not space-time block coding of STBC.

An embodiment of the present invention provides an OFDM system and method that can be used by applying the two modes proposed in the OFDM symbol at the same time.

An apparatus for transmitting an OFDM system based on CIOD and DSFBC according to an embodiment of the present invention includes a modulator for modulating an input data stream, a demultiplexer for splitting the modulated data stream into two streams, and A delay unit for delaying and outputting two streams by a predetermined delay time according to a mode, two encoders respectively receiving and encoding the two streams from the delay unit, and a signal encoded through the encoders in the mode And a converse rotation unit for converting the constellation rotated constellation and the encoded signal rotated in the constellation to a signal on the time axis.

At this time, the mode is characterized in that the space-frequency block codes (SFBC) -OFDM mode or coordinate interleaved orthogonal design (CIOD) -OFDM mode.

The constellation rotation unit rotates the constellation by the preset constellation rotation when the mode is the CIOD-OFDM mode, and when the mode is the DSFBC-OFDM mode, the encoded signal. It is characterized by outputting the signal without rotating the constellation.

The present invention provides a full-rate full-diversity while ensuring diversity order 4 which is a measure of link level performance of the MIMO system by effectively deriving transmission diversity when there are two or more transmission antennas or less than four and more than the reception antennas. Get a double data rate. In addition, it is easy to allocate data for each subcarrier for each mode according to the OFDM system. The low complexity of the receiver makes it easy to implement.

1 is a diagram illustrating a configuration of an OFDM system based on CIOD and DSFBC.
2 is a diagram illustrating a matrix X arrangement according to a CIOD-OFDM symbol period.
3 is a diagram illustrating matrix X placement according to a DSFBC-OFDM symbol period.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The present invention corresponds to SFBC-OFDM technology for applying multiple antennas to an OFDM system and is called a CIOD / DSFBC-OFDM transmitter. The proposed transmission mode has two modes, the first is coordinate interleaved orthorgonal design orthogonal frequency division multiplexing (CIOD-OFDM) mode and the second is double space frequency block code orthogonal frequency division multiplexing (DSFBC-OFMD) mode. Specifically, two to four transmission antennas are mainly applicable, and in the case of CIOD-OFDM mode, this transmission mode can be applied. The proposed CIOD-OFDM mode supports full-rate full diversity and supports single symbol decodability (ie low complexity decoding). Here, full rate means that there is no decrease in transmission rate. That is, it means that 4 symbols are received from 4 transmit antennas for 4 time samples, which is the same as the data rate of transmitting 1 symbol from 1 transmit antenna. The existing proposed similar transmission multiple antenna scheme does not support the aforementioned full-rate full diversity and single symbol decodability at the same time. DSFBC-OFDM mode can obtain twice the data rate compared to CIOD-OFMD.

1 is a diagram illustrating a configuration of an OFDM system based on CIOD and DSFBC. Referring to FIG. 1, a CIOD / DSFBC-OFDM system includes an OFDM transmitter 100 and an OFDM receiver 150.

First, the OFDM transmitter 100 includes a modulator 101, a demultiplexer 102, a delay unit 103, a first encoder 104, a second encoder 105, a constellation rotation unit 106, and a first 1 Inverse Fast Fourier Transformer (IFFT) 107, 2nd IFFT 108, 3rd IFFT 109, 4th IFFT 110, 1st CP Insertion 111, 2nd CP The inserter 112 includes a third CP inserter 113, a fourth CP inserter 114, and antennas 115 to 118.

The modulator 101 modulates an input data stream (data symbol) according to a corresponding modulation scheme (modulation level). In more detail, the modulator 101 maps an input data stream (data symbol) to a signal point by a corresponding modulation method (modulation level) and outputs complex symbols. For example, the modulation scheme includes binary phase shift keying (BPSK), which maps one bit (s = 1) to one signal point (complex symbol), and two bits (s = 2) to one complex symbol. Quadrature Quadrature Phase Shift Keying (QPSK), 8-ary Phase Shift Keying (8PSK) to map three bits (s = 3) to one complex symbol, and four bits (s = 4) to one complex symbol There are 16QAM for mapping and 64QAM for mapping 6 bits (s = 6) to one complex symbol.

The demultiplexer 102 divides the complex symbols output from the modulator 101 into two complex symbol streams and outputs the divided symbols.

The delay unit 103 receives two complex symbol streams output from the demultiplexer 102 and outputs the two complex symbol streams to the encoders 104 and 105 after a predetermined delay for each of two modes. At this time, the types of modes are CIOD-OFDM mode and DSFBC-OFDM mode. Mode delay will be described later in more detail when describing the operation of each mode.

The encoders 104 and 105 encode and output the complex symbol stream input from the delay unit 103 according to the encoding method according to the mode. Mode encoding will be described later in more detail when describing the operation of each mode.

The constellation rotation unit 106 outputs the encoded signal to the IFFTs 107 to 110 by performing a predetermined constellation rotation according to the mode. At this time, the types of modes are CIOD-OFDM mode and DSFBC-OFDM mode. The constellation rotation for each mode will be described later in more detail when describing the operation of each mode.

The IFFTs 107 to 110 convert the encoded constellation rotated signal into a signal on a time axis and output the converted signal.

The CP insertion units 111 to 114 insert a CP into guard intervals of signals received from the IFFTs 107 to 110 and output the CPs through the antennas 115 to 118.

The OFDM receiver 150 may include a first CP remover 151, a second CP remover 152, a first Fourier transformer (FFT) 153, a second FFT 154, The decoder 155 includes a constellation reverse rotation unit 156, a multiplexer 157, and a demodulator 158.

The CP removing units 151 and 152 remove the CP from the data received through the antenna and provide the CPs to the FFTs 153 and 154.

The FFTs 153 and 154 convert the received data from which the CP has been removed to data in the frequency domain through Fourier transform.

The decoder 155 receives the data of the frequency domain transformed through the FFTs 153 and 154 and decodes and outputs the data according to a decoding method according to a mode. At this time, the types of modes are CIOD-OFDM mode and DSFBC-OFDM mode. Mode decoding will be described later in more detail when describing the operation of each mode.

The constellation reverse rotation unit 156 performs a reverse constellation rotation preset according to the mode and outputs the decoded signal received from the decoder 155 to the multiplexer 157. At this time, the types of modes are CIOD-OFDM mode and DSFBC-OFDM mode. Constellation reverse rotation for each mode will be described later in more detail when describing the operation of each mode.

The multiplexer 157 multiplexes a signal received from the constellation reverse rotation unit 156 and outputs the multiplexed signal to the demodulator 158.

The demodulator 158 demodulates and outputs the signal received from the multiplexer 157 according to the modulation scheme of the OFDM transmitter 100.

Two modes of the CIOD / DSFBC-OFDM system, CIOD-OFDM mode and DSFBC-OFDM mode, will be described in each mode.

First, referring to the CIOD-OFDM mode, the CIOD-OFDM mode corresponds to a space-frequency coding technique that obtains full-diversity when two or more transmit antennas are applied by the CIOD / DSFBC-OFDM system.

The CIOD / DSFBC-OFDM system of FIG. 1 is similar to the overall Double STBC-OFDM. In FIG. 1, the modulated signal is divided into two streams and IFFT (inverse Fourier transform) is performed after space-time transmit diversity coding proposed by Alamouti in the frequency domain. However, an artificial delay is applied to each stream. This coding process is shown in Equation 1 below.

Here, the matrix S means that four symbols s0, s1, s2, and s3 are transmitted for two OFDM symbol times. A column of the matrix S denotes an antenna (space) to be transmitted as shown in FIG. 1, and a row denotes a subcarrier of each OFDM symbol. The peculiarity is that odd numbers are assigned to the same OFDM symbol and odd rows are even. Here, the allocation for each subcarrier is the same as the example of FIG. 2 is a diagram illustrating a matrix X arrangement according to a CIOD-OFDM symbol period.

Therefore, the transmitter has a structure using four transmit antennas and two OFDM symbol time periods. Data allocation for subcarrier f0 in OFDM symbols 1 and 2 transmits only antenna 0 and antenna 1, and likewise, only antenna 0 and antenna 1 load data in subcarrier at f1. The next subcarrier fn / 2 to the last subcarrier fn-1 load data only to antennas 2 and 3.

In FIG. 1, the constellation rotation unit 106 performs dynamics of interleaving the imaginary parts of the elements of the matrix S and then rotating each phase. The process of interleaving is shown in Equation 2 below.

Here, each phase roation value is exactly radian, arctan (2) / 2. This is the result of multiplying 0.8507 + j0.5257 by the complex number. This phase rotation is intended to be applied to obtain full diversity.

In the CIOD-OFDM mode, the reception apparatus 150 may demodulate only one reception antenna, unlike in FIG. 1. In addition, the number of the receiving antennas is not limited. In the present invention, when considering the CIOD-OFDM mode, when the decoding process of the received signal is expressed mathematically, it will be described in consideration of the case of one receiving antenna. Like the transmitting device 100, the receiving device 150 needs to receive and process a received signal for 2 symbol times. The signal received for 2 symbol time may be expressed as Equation 3 below.

Here, the received signal matrix r means a signal after the FFT process in FIG. 1. In addition, h vector represents a gain value of a wireless channel. When h is a matrix, there are two or more reception antennas. Since CIOD is assumed to have one receiving antenna, it is expressed as a vector in Equation 3, where h0 is the gain when the radio is transmitted from the first antenna to the receiving antenna, and h1 is the radio channel from the second antenna. Gain is delivered to the receiving antenna (h2 and h3 are the third and fourth respectively). Therefore, in the case of Equation 10, h_13 is a gain value experienced in the wireless channel by the signal transmitted from the fourth transmit antenna to the second receive antenna. vector n represents a Gaussian noise vector.

The transmitting end is transmitted as in Equation 3, but can be equivalently expressed as in Equation 4.

This equivalent representation has the advantage of being easily expressed in equations at the receiving end and can be simplified in practice.

The process of decoding / separating the received signal by processing the linear combination is shown in Equation 5. First, if the received signal r is given a channel estimate and a matrix product, the transmitted signal is separated into components multiplied by the power of the pair channel.

The decoded received signal undergoes a de-interleaving process, thereby obtaining additional diversity gain. The de-interleaving process is shown in Equation 6 below.

And finally, the process of decoding the received signal is shown in Equation 7 below.

In Equation 7, C denotes all possible symbols of the phase rotaded constellation. For example, in the case of QPSK, it becomes one of four as shown in Equation 8 below.

Thus, by substituting all existing symbols and finding the minimum value, it is the estimated transmitted signal. Then find the rotated constellation corresponding to s0, s1, s2, and s3. Then, the receiver 150 of FIG. 1 is input to the constellation reverse rotation unit 156, and after the phase de-rotation is performed with a general M-PSK or M-QAM signal, passes through the multiplexer 157 and finally returns. The grandfather 158 demodulates. In conclusion, the performance of the CIOD-OFDM mode can obtain diversity order 4 when there is only one receiving antenna.

The following describes the transmission process of the transmitting device 100 for the DSFBC. Unlike the CIOD-OFDM mode, the DSFBC-OFDM mode requires two or more receiving antennas to achieve a reasonable performance. However, in the case of CIOD, the delay of the transmitted signal is given as shown in <Equation 1> in the block that handles delay, while in DSFBC, it is transmitted as shown in <Equation 9> without such delay.

As shown in FIG. 3, mapping for each subcarrier is defined. 3 is a diagram illustrating matrix X placement according to a DSFBC-OFDM symbol period.

However, unlike CIOD, the constellation rotation unit 106 does not provide a separate constellation rotation. When there are two receiving antennas of the receiving device 150, the received signal may be expressed as Equation 10 below.

Here, h vector represents a gain value of a wireless channel. When h is a matrix, there are two or more reception antennas. h13 represents a gain value experienced in the wireless channel by the signal transmitted from the fourth transmit antenna to the second receive antenna. vector n represents a Gaussian noise vector.

Like CIOD, a received signal can be equivalently expressed as in Equation 11 below. Here, the row of the channel transfer function matrix H indicates the order of receive antennas and the column indicates the order of transmit antennas.

As shown in Equation 11, a signal input to each receiving antenna is composed of a sum of a signal obtained by multiplying each transmission signal by a channel transfer function and a noise of the reception device 150 on a wireless fading channel. The reception demodulation process can be obtained by inversing the channel matrix.

First, QR decomposition is performed based on the channel matrix arranged in Equation (11). The result can be developed as shown in Equation 12 below.

As shown in Equation 12, the R matrix has an upper triangular form, and the value of R23 is calculated as 0. This is because the channel matrix is possible in the double SFBC structure. Next, the transmission signal is estimated through the following equation (13).

The estimated signal is bypassed in the constellation reverse rotation unit 156 of FIG. 1 without passing through the constellation reverse rotation and input to the multiplexer 157 and finally demodulated by the demodulator 158.

The methods according to embodiments of the present invention may be implemented in the form of program instructions that can be executed through various computer means and recorded in a computer-readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the present invention or may be available to those skilled in the art of computer software.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the claims below but also by the equivalents of the claims.

Claims (1)

A modulator for modulating an input data stream;
A demultiplexer for dividing the modulated data stream into two streams;
A delay unit for delaying and outputting the two streams by a predetermined delay time according to a mode;
Two encoders each receiving and encoding the two streams from the delay unit;
A constellation rotation unit rotating constellations according to the mode of the signal encoded by the encoders; And
An inverse Fourier transform unit converting the constellation rotated encoded signal into a signal on a time axis and outputting the converted signal;
Transmission apparatus of OFDM system based on CIOD and DSFBC.

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