KR20080105822A - Apparatus and method for transmitting and receiving signal multiple input multiple output broadband wireless communication system - Google Patents

Abstract

An apparatus and a method for transmitting and receiving a signal in a MIMO(Multiple Input Multiple Output) broadband wireless communication system are provided to increase the gain of diversity in an MIMO broadband wireless communication system. A transmitting apparatus in an MIMO broadband wireless communication system comprises: a first encoder(240-1) which Alamouti-encodes complex symbols of Nc/n number, which are to be transmitted through a pair of first antennas, repeatedly n times; a second encoder(240-2) which Alamouti-encodes complex symbols of Nc/n number, which are to be transmitted through a pair of second antennas, repeatedly n times; and plural RF(Radio Frequency) transmitters(260-1 to 260-4) which transmits Alamouti-encoded complex symbols which are mapped on subcarrier of Nc number.

Description

Signal transceiving device and method in multi-input wideband wireless communication system {APPARATUS AND METHOD FOR TRANSMITTING AND RECEIVING SIGNAL MULTIPLE INPUT MULTIPLE OUTPUT BROADBAND WIRELESS COMMUNICATION SYSTEM}

1 is a diagram illustrating an example of a transmission symbol for each antenna in a multiple input / output broadband wireless communication system according to the present invention;

2 is a block diagram of a transmitter in a multiple input / output broadband wireless communication system according to an embodiment of the present invention;

3 is a block diagram of a receiving end in a multiple input / output broadband wireless communication system according to an embodiment of the present invention;

4 is a block diagram of a signal detector in a multiple input / output broadband wireless communication system according to an embodiment of the present invention;

5 is a diagram illustrating a signal transmission procedure of a transmitter in a multiple input / output broadband wireless communication system according to an embodiment of the present invention;

6 is a diagram illustrating a signal detection procedure of a receiver in a multiple input / output broadband wireless communication system according to an embodiment of the present invention;

7 illustrates the performance of a transmit / receive technique in accordance with the present invention.

The present invention relates to a multiple input multiple output (hereinafter referred to as "MIMO") broadband wireless communication system, and more particularly, to an apparatus and method for transmitting and receiving signals in a MIMO broadband wireless communication system.

The 4th Generation (hereinafter referred to as '4G') communication system provides users with services of various quality of service (QoS) using a transmission rate of about 100 Mbps. There is active research going on. A representative communication system of the 4G communication system is an Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system. The IEEE 802.16 communication system uses orthogonal frequency division multiplexing (OFDM) / orthogonal frequency division to support a broadband transmission network on a physical channel of the wireless communication system. A communication system employing an Orthogonal Frequency Division Multiple Access (hereinafter referred to as 'OFDMA') scheme.

In addition, as one of technologies for satisfying the demand for high speed and high quality data transmission, MIMO technology using a plurality of transmit and receive antennas has been greatly attracting attention. The MIMO technology is a technology that can significantly improve the channel capacity than using a single antenna by performing communication using a plurality of streams through a plurality of antennas. For example, if both transmitting and receiving stages use M transmit and receive antennas, the channels between each antenna are independent, and the bandwidth and total transmit power are fixed, the average channel capacity is increased by M times compared to the case of a single antenna. Done.

An example of a transmission scheme using both the OFDM system and the MIMO technique is a double space time transmit diversity (OFDM) scheme. The DSTTD-OFDM technique is a technique of obtaining spatial multiplexing gain by performing two Alamouti encodings in parallel, that is, performing allamutation encoding on two pairs of streams, respectively. In the case of performing the Alamouti encoding, the receiving end has an optimal reception performance due to the orthogonality of the Alamouti code, even if only the Channel Matched Filter is used.

Techniques for receiving a signal transmitted using the DSTTD-OFDM technique include Zero Forcing (ZF), Minimum Mean Square Error (MMSE), Decision Feedback (DF), Maximum Likelihood (ML), and the like. Here, the ML technique shows optimal performance but has a very large complexity. In comparison, the ZF and MMSE techniques have low complexity but very low performance compared to the ML technique. In addition, the DF technique has only a simple signal-to-noise ratio gain compared to the ZF and MMSE techniques. Therefore, it is required to propose an effective transmission and reception technique using both the OFDM scheme and the MIMO technique.

Accordingly, an object of the present invention is to provide a transmission and reception apparatus and method using both an orthogonal frequency division multiplexing (OFDM) scheme and a MIMO technique in a multiple input multiple output (MIMO) broadband wireless communication system.

Another object of the present invention is to provide an apparatus and method for increasing diversity gain in a MIMO broadband wireless communication system.

It is still another object of the present invention to provide an apparatus and method for increasing the interference cancellation effect in a signal transmitted through the other antenna by improving the detection accuracy of a signal transmitted through some antenna in a MIMO broadband wireless communication system.

It is still another object of the present invention to provide an apparatus and method for repeating a signal transmitted through some antennas on a frequency axis in a MIMO broadband wireless communication system.

Another object of the present invention is to provide an apparatus and method for adjusting transmission power for each antenna in a MIMO broadband wireless communication system.

According to a first aspect of the present invention for achieving the above object, in a MIMO wideband wireless communication system, the transmitting apparatus encodes N _c complex symbols to be transmitted through a first antenna pair (Alamouti) encoding. A first encoder (Encoder), a second encoder for repeating alamati encoding n _c / n complex symbols to be transmitted through a second antenna pair n times, and an alamiti mapped to each of the N _c subcarriers And a plurality of transmitters for transmitting the encoded complex symbols.

According to a second aspect of the present invention for achieving the above object, in the MIMO broadband wireless communication system, the receiving device is mapped to each of the N _c subcarriers to combine the signals received through the first antenna pair according to the repetition interval A combiner for generating N _c / n combined signals, a first detector for detecting transmission signals through the first antenna pair from the combined signals, and a first antenna in the received signals through a second antenna pair And a second detector for detecting a transmission signal through the second antenna pair from the interference-received received signals.

According to a third aspect of the present invention for achieving the above object, a signal transmission method of a transmitter in a MIMO wideband wireless communication system includes a process of performing Alamati encoding of N _c complex symbols to be transmitted through a first antenna pair; And repeating alamute encoding of n _c / n complex symbols to be transmitted through 2 antenna pairs n times, and transmitting alamuti encoded complex symbols mapped to each of the N _c subcarriers. do.

According to a fourth aspect of the present invention for achieving the above object, a signal detection method of a receiver in a MIMO broadband wireless communication system, the signals received through the first antenna pair to be mapped to each of the N _c subcarriers at a repetitive interval Combining to generate N _c / n combined signals; detecting transmission signals through the first antenna pair from the combined signals; and receiving first signals from the second antenna pair. And removing the interference due to the transmission signals through the antenna pair, and detecting the transmission signal through the second antenna pair from the interference-received received signals.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Hereinafter, the present invention describes a technique for transmitting and receiving signals in a multiple input multiple output (MIMO) broadband wireless communication system. The present invention is described by taking an orthogonal frequency division multiplexing (hereinafter referred to as "OFDM") wireless communication system as an example, and may be equally applicable to other wireless communication systems. In addition, hereinafter, the present invention will be described assuming a transmitter having four transmission antennas and a receiver having four reception antennas for convenience of description.

In general, the transmitting end according to the Double Space Time Transmit Diversity-OFDM (DSTTD-OFDM) scheme encodes a transmission symbol using a code such as Equation (1).

In Equation 1, C ^k denotes an encoding matrix, and S _n ^k denotes a k-th complex symbol of an n-th stream. That is, the transmitting end generates eight transmission symbols by encoding four complex symbols to be transmitted through each stream through the matrix of Equation (1).

In this case, an equivalent channel matrix between the transmitting end and the receiving end is expressed by Equation 2.

In Equation 2, y ^k is a received signal vector of a k-th subcarrier, H _eff ^k is an equivalent channel matrix of a k-th subcarrier, s _k is a transmission signal vector of a k-th subcarrier, and n _k is k. The noise of the first subcarrier, h _ij ^k, refers to a channel frequency response between the j th transmit antenna and the i th receive antenna in the k th subcarrier.

The receiver performs QR Decomposition on the equivalent channel matrix as shown in Equation 3 to perform Decision Feedback (DF) detection.

,

,

In Equation 3, H _eff ^k denotes an equivalent channel matrix of the k-th subcarrier, and R _ij ^k denotes an element of row i and j of R ^k .

Using the characteristic shown in Equation (3), the receiver can simply detect the complex symbols transmitted through the lower antenna pair (Pair) by multiplying the received signal vector by (Q ^k ) ^H. The receiver may detect the complex symbols transmitted through the upper antenna pair by removing components of the detected signal from the received signal for the upper antenna pair. At this time, the detection accuracy of the complex symbols transmitted through the lower antenna pair affects the detection accuracy of the complex symbols transmitted through the upper antenna pair. In other words, if the detection of the complex symbols transmitted through the lower antenna pair is incorrect, the detection of the complex symbols transmitted through the upper antenna pair is also likely to be incorrect.

Accordingly, the transmitter according to the present invention repeatedly transmits a transmission symbol on the frequency axis in order to improve detection accuracy of complex symbols transmitted through the lower antenna pair. That is, as shown in FIG. 1, the transmitting end transmits N _c complex symbols through antenna A and antenna B, and repeatedly transmits N _c / 2 complex symbols on the frequency axis through antenna C and antenna D, respectively. do. Here, N _c is the number of subcarriers. Accordingly, when the encoding matrix is redefined, Equation 4 is obtained.

In Equation 4, C ^k is an encoding matrix, S _n ^k is a k-th complex symbol of an nth stream, and N _c is a number of subcarriers.

In this case, due to the repeated transmission of the complex symbol in the lower antenna pair, spectrum efficiency loss occurs. Accordingly, the transmitter increases the modulation order of complex symbols to be transmitted through the upper antenna pair to compensate for the spectral efficiency loss. That is, the transmitter modulates data to be transmitted to the lower antenna pair by applying a higher order modulation scheme than a modulation order applied to bit string modulation to be transmitted through the lower antenna pair. For example, if the bit stream to be transmitted through the lower antenna pair is modulated by a quadrature phase shift keying (QPSK) scheme, the transmitter may transmit a bit stream to be transmitted through the upper antenna pair to a 16 quaurature amplitude modulation (16QAM) scheme. Modulate.

Here, the increase in the modulation order of the bit stream to be transmitted through the upper antenna pair is valid for the following reason. Since the detection accuracy of the complex symbol transmitted through the lower antenna pair is increased through repetitive transmission, the receiving end can accurately identify the interference component of the received signal through the upper antenna pair. Thus, the receiving end can perform interference cancellation more accurately in the received signal through the upper antenna pair, which can be regarded as a result of reduced interference in the channel of the upper antenna pair.

Accordingly, the receiver first detects by combining the signals repeatedly transmitted through the lower antenna pair. After receiving the interference due to the detected signal, the receiving end detects the transmission signals through the upper antenna pair. When the signal combination of the receiver is expressed by an equation, Equation 5 is obtained.

는 i번째 안테나를 통해 송신된 신호 중 k번째 부반송파 및 (k+N_c/2)번째 부반송파 수신신호의 결합신호, 상기

는 i번째 안테나를 통해 송신된 신호 중 k번째 부반송파 수신신호, 상기 R^k _ii는 k번째 부반송파에 대한 등가 채널행렬을 QR 분해하여 얻어지는 R행렬의 i행 i열 원소, 상기 s^k _i는 i번째 안테나를 통해 송신된 신호 중 k번째 부반송파 송신신호, 상기 n_k'는 k번 째 부반송파의 잡음을 의미한다.In Equation 5,

Is a combined signal of the k th subcarrier and the (k + N _c / 2) th subcarrier received signal among the signals transmitted through the i th antenna,

Is a k-th subcarrier received signal of the signal transmitted through the i-th antenna, wherein R ^k _ii is an i-th column i column element of the R matrix obtained by QR decomposition of an equivalent channel matrix for the k-th subcarrier, and s ^k _i is the i-th The k th subcarrier transmission signal of the signal transmitted through the antenna, n _k 'means the noise of the k th subcarrier.

In addition to the repetitive transmission, the transmitter according to the present invention improves system performance by adjusting the transmission power for each antenna. The criterion of the transmission power adjustment is shown in Equation 6.

는 평균 비트오류율, 상기 λ는 라그랑즈 승수(Lagrange Multiplier)를 의미한다. 즉, 상기 <수학식 6>은 상기

을 제한 조건으로 하여 상기

을 최소화하는 P₁, P₂, P₃, P₄를 찾아내고자 하는 의미이다.In Equation (6), J (·) is Cost Funtion, P _i is the transmit power of the i-th antenna, and

Is an average bit error rate, and [lambda] is a Lagrange multiplier. That is, Equation 6 is

On the condition that

This is to find P ₁ , P ₂ , P ₃ and P ₄ that minimize the

The solution to Equation 6 is the same as Equation 7.

In Equation 7, P _i is a value determined according to a transmission power of an i th antenna, and α _i and β _i are an approximation equation of an error rate for a corresponding modulation scheme. This value is included.

For example, the approximation equation of the error rate has the form as shown in Equation (8).

In Equation 8, P _b is a bit error rate, α And β denotes an approximation coefficient, h denotes a channel coefficient between a transmitting and receiving end, and ρ denotes a signal to noise ratio (SNR).

2 is a block diagram of a transmitter in a multiple input / output broadband wireless communication system according to an exemplary embodiment of the present invention.

As shown in FIG. 2, the transmitter has a first modulator 210-1, a second modulator 210-2, a symbol copyer 220, a power allocator 230, and a plurality of Alamouti encoders. Encoders 240-1 and 240-2, a plurality of OFDM modulators 250-1 to 250-4, and a plurality of RF (Radio Frequency) transmitters 260-1 to 260-4 do.

The first modulator 210-1 modulates the bit string to be transmitted through the upper antenna pair, and the second modulator 210-2 modulates the bit string to be transmitted through the lower antenna pair. However, the first modulator 210-1 uses a higher order modulation scheme than the second modulator 210-2.

The symbol copyer 220 copies the complex symbols provided from the second modulator 210-2 so that one OFDM symbol includes the same complex symbols repeatedly. That is, the symbol copyer 220 outputs N _c complex symbols by copying and connecting N _c / n complex symbols to n. For example, like the complex symbol sequence of the antennas C and D shown in FIG. 1, the symbol copyer 220 copies and connects the complex symbols so that the complex symbols are repeatedly inserted twice in one OFDM symbol. Here, the number of repetitions of the complex symbols may vary according to embodiments.

The power allocator 230 determines the transmit power of each antenna and adjusts the signal size according to the determined transmit power. The power allocator 230 determines transmission power of each antenna according to Equation (7). Each of the plurality of alamuti encoders 240-1 and 240-2 encodes the complex symbols to be transmitted through a corresponding antenna pair. For example, when the complex symbols to be transmitted through the lower antenna pair are repeated twice, the plurality of Alamouti encoders 240-1 and 240-2 are encoded using a matrix such as Equation 4 above. do.

Each of the plurality of OFDM modulators 250-1 through 250-4 converts complex symbols to be transmitted through corresponding antennas into OFDM symbols through an inverse fast fourier transform (IFFT) operation. Each of the plurality of RF transmitters 260-1 to 260-4 converts and amplifies a signal from a corresponding OFDM modulator into an RF band signal and transmits the same through an antenna.

3 is a block diagram of a receiver in a multiple input / output broadband wireless communication system according to an exemplary embodiment of the present invention.

As shown in FIG. 3, the receiver includes a plurality of RF receivers 310-1 to 310-4, a plurality of OFDM demodulators 320-1 to 320-4, a channel estimator 330, and an equivalent channel. The matrix constructor 340, the QR decomposer 350, and the signal detector 360 are configured.

Each of the plurality of RF receivers 310-1 to 310-4 converts an RF band signal received through a corresponding antenna into a baseband signal. Each of the plurality of OFDM demodulators 320-1 to 320-4 converts OFDM symbols from corresponding RF receivers into complex symbols for each subcarrier through a fast fourier transform (FFT) operation.

The channel estimator 330 estimates a channel with a transmitter using the received signal. In other words, the channel estimator 330 estimates a channel for each antenna and a subcarrier using a predetermined signal, such as a pilot symbol. The equivalent channel matrix configurator 340 constructs an equivalent channel matrix using the estimated channel information. Here, the equivalent channel matrix has a form as shown in Equation 2. The QR decomposer 350 performs QR decomposition on the equivalent channel matrix to calculate a Q matrix and an R matrix. Here, the R matrix has the form as shown in Equation 3 above.

The signal detector 360 detects a transmission signal by using the Q matrix and the R matrix provided from the QR decoder 350 and the received signals provided from the OFDM demodulators 320-1 to 320-4. . In particular, according to the present invention, the signal detector 360 detects the transmission signal using the repeated transmission of the received signal through the lower antenna pair. Detailed configuration and function of the signal detector 360 will be described below with reference to FIG. 4.

4 is a block diagram of a signal detector in a multiple input / output broadband wireless communication system according to an exemplary embodiment of the present invention.

As shown in FIG. 4, the signal detector 360 includes a matrix multiplier 402, a plurality of signal combiners 404-1 and 404-2, a first detector 406, an interference canceller 408, and a second detector. It comprises a two detector 410.

The matrix multiplier 420 transforms the received signal matrix into a product of the matrix R and the transmitted signal by multiplying the received signal matrix by the Q ^H matrix. Each of the plurality of signal combiners 404-1 and 404-2 combines the signals received through each of the lower antenna pairs according to a repetition interval. For example, when the transmitting end repeats the complex symbols twice as shown in FIG. 1, each of the plurality of signal combiners 404-1 and 404-2 is the (m) th and (N _c / 2). + m) combines the th signal.

The first detector 406 detects a transmission signal through the lower antenna pair. In other words, the first detector 406 detects a transmission signal from the combined signal using the characteristics of the R matrix. For example, when the R matrix is equal to Equation 3, the first detector 406 detects the transmission signal by dividing each of the modified received signals corresponding to the lower antenna pair by R ^k ₃₃ . . In addition, the first detector 406 provides the detected transmission signal to the interference canceller 408.

The interference canceller 408 removes interference due to the transmission signal through the lower antenna pair from the modified received signal corresponding to the upper antenna pair. That is, the interference canceller 408 subtracts the product of the transmitted signal detected from the modified received signal corresponding to the upper antenna pair and the corresponding R matrix element. For example, when the R matrix is equal to Equation 3, the interference canceller 408 multiplies the detected signals by -R ^{k *} ₁₄ and R ^{k *} ₁₃ , respectively, and then corresponds to the second antenna. The multiplication result is subtracted from the modified received signal. The interference canceller 408 multiplies the detected signals by R ^k ₁₃ and R ^k ₁₄ , respectively, and then subtracts the multiplication result value from the modified received signal corresponding to the first antenna.

The second detector 410 detects a transmission signal through an upper antenna pair. In other words, the second detector 410 detects a transmission signal from the interference canceled signal provided from the interference canceller 408 by using the characteristics of the R matrix. For example, when the R matrix is equal to Equation 3, the second detector 410 detects a transmission signal by dividing each of the interference canceled signals by R ^k ₁₁ .

5 illustrates a signal transmission procedure of a transmitter in a multiple input / output broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 5, in step 501, the transmitter generates N _c / n complex symbols to be transmitted through a lower antenna pair. Here, N _c is the number of subcarriers. And, n is an arbitrary integer, which is a preset value.

Subsequently, the transmitter proceeds to step 503 to generate N _c complex symbols to be transmitted through the higher antenna pair. However, the transmitting end generates complex symbols by using a higher order modulation method than in step 501.

After generating the complex symbols, the transmitter proceeds to step 505 to alamutely encode N _c / n complex symbols to be transmitted through a lower antenna pair n times, and then encode encoded complex symbols to N _c subcarriers. Map it.

Subsequently, the transmitter proceeds to step 507 by alamuty encoding N _c complex symbols to be transmitted through the higher antenna pair and mapping the encoded complex symbols to N _c subcarriers.

After mapping the complex symbols to subcarriers, the transmitter proceeds to step 509 to generate an OFDM symbol through an IFFT operation.

In step 511, the transmitter calculates power factor for each antenna. For example, the transmitter may calculate the power factor of each antenna according to Equation (7).

After calculating the power factor, the transmitter proceeds to step 513 to convert the OFDM symbols into an RF band signal and transmits the data through a corresponding antenna.

6 illustrates a signal detection procedure of a receiver in a multiple input / output broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 6, the receiver checks whether a signal is received through a plurality of antennas in step 601.

When the signal is received, the receiver proceeds to step 603 to estimate a channel with the transmitter and configure an equivalent channel matrix. Here, the equivalent channel matrix has a form as shown in Equation 2.

After configuring the equivalent channel matrix, the receiver proceeds to step 605 to QR-decompose the equivalent channel matrix to generate a Q matrix and an R matrix. Here, the R matrix has the form as shown in Equation 3 above.

After performing the QR decomposition, the receiver proceeds to step 607 to multiply the received signal by a Q ^H matrix to transform the received signal into a product of an R matrix and a transmitted signal.

In step 609, the receiving end combines the modified received signal corresponding to the lower antenna pair according to the repetition interval. For example, when the transmitting end repeats the complex symbols twice as shown in FIG. 1, the receiving end combines the (n) th and (N _c / 2 + n) th signals.

After combining the modified received signal corresponding to the lower antenna pair, the receiver proceeds to step 611 to detect a transmission signal through the lower antenna pair. In other words, the receiving end detects a transmission signal from the combined signal using the characteristics of the R matrix. For example, when the R matrix is equal to Equation 3, the receiver detects a transmission signal by dividing each of the modified reception signals corresponding to the lower antenna pair by R ^k ₃₃ .

After detecting the transmission signal through the lower antenna pair, the receiver proceeds to step 613 to remove interference due to the transmission signal through the lower antenna pair from the modified received signal corresponding to the upper antenna pair. That is, the receiving end subtracts the product of the transmitted signal detected from the modified received signal corresponding to the upper antenna pair and the corresponding R matrix element. For example, when the R matrix is equal to Equation 3, the receiver multiplies the detected signals by -R ^{k *} ₁₄ and R ^{k *} ₁₃ , respectively, and then receives a modified reception corresponding to the second antenna. Subtracts the result of the multiplication from the signal. The receiver multiplies the detected signals by R ^k ₁₃ and R ^k ₁₄ , respectively, and subtracts the multiplication result from the modified received signal corresponding to the first antenna.

After removing the interference, the receiver proceeds to step 615 to detect the transmission signal through the upper antenna pair. In other words, the receiving end detects a transmission signal from the interference canceled signal using the characteristics of the R matrix. For example, when the R matrix is equal to Equation 3, the receiver detects a transmission signal by dividing each of the interference canceled signals by R ^k ₁₁ .

The above-described embodiment has been described assuming a transmitting end and a receiving end having four transmitting antennas and receiving antennas, that is, two pairs of transmitting and receiving antennas, respectively. However, the present invention can be equally applied to a transmitter and a receiver having three or more pairs of transmit and receive antennas. If three or more pairs of transmit / receive antennas exist, the transmitter performs repetitive transmission on at least one antenna pair. The transmitter modulates a bit string to be transmitted through antenna pairs that are not repeatedly transmitted in a relatively high order modulation scheme. That is, when three or more pairs of transmit / receive antennas exist, the number of antenna pairs to which the repetitive transmission is to be applied may vary depending on the intention of the person implementing the present invention.

7 illustrates the performance of a transmit / receive technique in accordance with the present invention. 7 illustrates a graph of simulation results of a system to which a transmission and reception technique according to the present invention is applied. In the simulation, the total bandwidth is set to 20 MHz, the number of subcarriers is 64, the cyclic prefix (CP) is 16 samples, and the radio channel is set to an exponential decay channel.

7 illustrates the bit error rate according to the bit energy-to-noise ratio (E _b / N ₀ ). As shown in FIG. 7, the transmission and reception technique according to the present invention exhibits a lower bit error rate than the conventional DF technique. In other words, when the transmission / reception scheme according to the present invention is used, a performance improvement of 3.7 dB appears at a bit error rate of 10 ⁻⁴ as compared with the conventional DF scheme. In addition, when the power control for each antenna is performed, a performance improvement of about 1 dB appears compared to the case where the power control for each antenna is not performed.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, in the Multiple Input Multiple Output (MIMO) broadband wireless communication system, by performing repeated transmission and power control for each antenna pair for the lower antenna pair, the transmission / reception performance of the system can be improved with low complexity.

Claims (30)

Multiple Input Multiple Output (MIMO) In a transmission apparatus in a broadband wireless communication system, A first encoder (Alamouti) encoding N _c complex symbols to be transmitted through a first antenna pair (Pair), A second encoder for alamutically encoding N _c / n complex symbols to be transmitted through the second antenna pair n times; And a plurality of transmitters for transmitting alamuti-encoded complex symbols mapped to each of the N _c subcarriers. The method of claim 1, It further comprises a plurality of OFDM modulators for generating the Orthogonal Frequency Division Multiplexing (OFDM) symbol by arranging the alamuty encoded complex symbols from the first encoder and the second encoder on the frequency axis and performing an Inverse Fast Fourier Transform (IFFT) operation Device characterized in that. The method of claim 1, A first modulator for generating complex symbols by modulating a bit stream to be transmitted through the first antenna pair; A second modulator for generating complex symbols by modulating the bit stream to be transmitted through the second antenna pair, And the first modulator uses a higher order modulation scheme than the second modulator. The method of claim 1, And a copier that provides N _c complex symbols to the second encoder by copying and concatenating N _c / n complex symbols to be transmitted through the second antenna pair. The method of claim 1, And an allocator for allocating transmit power of each transmit antenna such that an average bit error rate is minimized. The method of claim 5, The allocator, characterized in that for determining the transmission power of each transmission antenna as shown in the following equation,

Here, P _i is the transmission power of the i-th antenna, α _i and β _i is a value determined according to the modulation order applied to the i-th antenna is a value included in the approximation formula of the error rate for the modulation method, The first antenna and the second antenna are the first antenna pair, the third antenna and the fourth antenna are the first antenna pair. Multiple Input Multiple Output (MIMO) In a receiving device in a broadband wireless communication system, A combiner mapped to each of the N _c subcarriers to combine the signals received through the first antenna pair according to a repetition interval to generate N _c / n combined signals; A first detector for detecting transmission signals through the first antenna pair from the combined signals; A canceller for removing interference due to the transmission signals through the first antenna pair from the reception signals through the second antenna pair; And a second detector for detecting a transmission signal through the second antenna pair from the interference canceled reception signals. The method of claim 7, wherein An estimator for estimating a channel with a transmitter using a received signal; A composer constituting an equivalent channel matrix using the estimated channel information, A decomposer for generating a Q matrix and an R matrix by QR decomposition of the equivalent channel matrix; And multiplying the received signal by a Q ^H matrix to transform the received signal into a product of the R matrix and the transmitted signal. The method of claim 8, The equivalent channel matrix is a device, characterized in that the form of the following formula,

Here, h _ij ^k denotes a channel frequency response between the j th transmission antenna and the i th reception antenna in the k th subcarrier. The method of claim 9, The R matrix is a device, characterized in that the form of the following formula,

Here, R _ij means an element of row i column j columns of the R matrix. The method of claim 10, The combiner combines each of the modified received signals corresponding to the first antenna pair from the multiplier, And the first detector detects a transmission signal through the first antenna pair by dividing each of the signals from the combiner by the R ₃₃ . The method of claim 10, The eliminator is And multiplying R ₁₃ and R ₁₄ by the transmission signals detected by the first detector, and subtracting the multiplication result from the modified reception signal corresponding to the second antenna pair. The method of claim 10, The eliminator is And multiplying the -R ^* ₁₄ and the R ^* ₁₃ by the transmission signals detected by the first detector, respectively, and subtracting the multiplication result from the modified reception signal corresponding to the second antenna pair. . The method of claim 10, The second detector, Detecting a transmission signal through the first antenna pair by dividing each of the interference canceled signals from the canceller by the R ₁₁ . The method of claim 7, wherein And an OFDM demodulator for restoring N _c complex symbols for each antenna by performing Fast Fouier Transform (FFT) operation on Orthogonal Frequency Division Multiplexing (OFDM) symbols received through each antenna. Multiple Input Multiple Output (MIMO) In a broadband wireless communication system, Alamouti encoding N _c complex symbols to be transmitted through a first antenna pair; Repeating n times alammut encoding N _c / n complex symbols to be transmitted through the second antenna pair, And transmitting alamuty encoded complex symbols mapped to each of the N _c subcarriers. The method of claim 16, And arranging the alamuti-encoded complex symbols on a frequency axis and performing an inverse fast fourier transform (IFFT) operation to generate an orthogonal frequency division multiplexing (OFDM) symbol. The method of claim 16, Generating complex symbols by modulating a bit string to be transmitted through the first antenna pair according to a first modulation scheme; The method may further include generating complex symbols by modulating a bit string to be transmitted through the second antenna pair according to a second modulation scheme. And wherein the first modulation method has a higher modulation order than the second modulation method. The method of claim 16, Determining the transmit power of each transmit antenna such that an average bit error rate is minimized. The method of claim 19, The transmission power of each transmission antenna is determined by the following formula,

Here, P _i is the transmission power of the i-th antenna, α _i and β _i is a value determined according to the modulation order applied to the i-th antenna is a value included in the approximation formula of the error rate for the modulation method, The first antenna and the second antenna are the first antenna pair, the third antenna and the fourth antenna are the first antenna pair. Multiple Input Multiple Output (MIMO) A method for detecting a signal at a receiver in a broadband wireless communication system, Generating N _c / n combined signals by combining the signals received through the first antenna pairs by repetition intervals mapped to each of the N _c subcarriers; Detecting transmission signals through the first antenna pair from the combined signals; Removing interference from signals transmitted through the first antenna pair from signals received through the second antenna pair; Detecting a transmission signal through the second antenna pair from the interference-received received signals. The method of claim 21, Estimating a channel with a transmitter using a received signal; Constructing an equivalent channel matrix using the estimated channel information, QR decomposition of the equivalent channel matrix to generate a Q matrix and an R matrix; And multiplying the received signal by a Q ^H matrix to transform the received signal into a product of the R matrix and the transmitted signal. The method of claim 22, The equivalent channel matrix is characterized in that the form of the following formula,

Here, h _ij ^k denotes a channel frequency response between the j th transmission antenna and the i th reception antenna in the k th subcarrier. The method of claim 23, wherein The R matrix is characterized in that the form of the following formula,

Here, R _ij means an element of row i column j columns of the R matrix. The method of claim 24, Generation of the combined signals, And using the modified received signals corresponding to the first antenna pair. The method of claim 25, The transmission signal through the first antenna pair is, And detecting each of the combined signals by dividing by R ₃₃ . The method of claim 26, The process of removing the interference, Multiplying the detected transmission signals by the R ₁₃ and the R ₁₄ , respectively; Subtracting a multiplication result from the modified received signal corresponding to the second antenna pair. The method of claim 26, The process of removing the interference, Multiplying the detected transmission signals by -R ^* ₁₄ and R ^* ₁₃ , respectively; Subtracting a multiplication result from the modified received signal corresponding to the second antenna pair. The method of claim 26, The transmission signal through the first antenna pair is, And detecting each of the interference canceled signals by the R ₁₁ . The method of claim 21, And restoring N _c complex symbols for each antenna by performing Fast Fouier Transform (FFT) operation on Orthogonal Frequency Division Multiplexing (OFDM) symbols received through each antenna.

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