KR20100022629A - Multi input multi output system and method of controlling the same - Google Patents

Abstract

PURPOSE: A multi input increasing the channel capacity in the limited frequency assignment is provided to secure efficient transmission rate by possessively deal with than the channel environment change. CONSTITUTION: A multi Input comprises MCS(Modulation and Coding Scheme) level selector(140), a modulation/coding unit(130) and D-STTD(Double-Space Time Transmit Diversity) encoder(300). According to the MCS level selection is the channel condition, the combination of the coding method and data modulation MCS(Modulation and Coding Scheme) level is selected. According to the modulation/coding method which the modulation/coding unit comes under to the MCS level, transmission data is processed. The D-STTD encoder codes transmission data in the D-STTD(Double-Space Time Transmit Diversity) mode.

Description

Multi input multi output system and method of controlling the same

An embodiment of the present invention relates to a multiple input / output communication system and a control method thereof.

Recent wireless communication technologies aim at various multimedia communications. Accordingly, as a method for increasing a transmission speed at a given bandwidth for high-speed data transmission, research on a multiple input multiple output (MIMO) system has been actively conducted. MIMO technology can increase the channel capacity within a limited frequency resource by using multiple antennas at both ends of the transmission and reception.

MIMO technology includes diversity technology and multiplexing technology. Diversity technology includes a space-time coding (STC) technology configured to obtain a space-time diversity gain using multiple transmit / receive antennas. Multiplexing technology includes a BLAST (Bell-lap Layered Space-Time) technology that transmits different data to each transmit antenna. Recently, D-STTD (Double-Space Time Transmit Diversity) technology has been developed to achieve the effects of diversity technology and multiplexing technology.

D-STTD technology is a combination of space multiplexing technology and STTD technology, and uses two space-time block codes (STBCs) each having a pair of antennas. D-STTD applies STTD by first creating two symbol strings by spatial multiplexing and assigning two antenna pairs to each symbol string. Therefore, a total of four transmit antennas are required for spatial multiplexing and STTD application, and two or more receive antennas are required to detect spatial multiplexed symbols. Since the D-STTD technology transmits four symbols during two symbol intervals, the same data rate as the spatial multiplexing technology using two transmission antennas can be obtained. In addition, since each antenna of the two pairs is used for the STTD, it has the same transmit diversity gain as the conventional STTD.

However, the D-STTD technology uses a constant channel coding rate and modulation technique regardless of the state change of the channel response. Therefore, in an environment where a certain amount of SNR is not secured, a low channel coding rate and a low modulation technique are fixed There is a problem to choose from.

An embodiment of the present invention provides a multi-input and output communication system and a control method thereof.

An embodiment of the present invention provides a multi-input and output communication system and a control method thereof, which can secure the most efficient transmission rate by more actively coping with a channel environment change, and can increase the channel capacity within a limited frequency resource.

A multi-input / output communication system according to an embodiment of the present invention includes: a Modulation and Coding Scheme (MCS) level selector for selecting an MCS level, which is a combination of data modulation and coding methods, according to a channel state; A modulation and coding unit for processing transmission data according to the modulation and coding method of the selected MCS level; And a D-STTD encoder for coding and transmitting the transmission data processed through the modulation and coding unit in a double-space time transmit diversity (D-STTD) scheme.

A control method of a multiple input / output communication system according to an embodiment of the present invention includes selecting an MCS level which is a combination of a data modulation and coding method according to a channel state; Modulating and coding transmission data according to the selected MCS level; And coding the modulated and coded transmission data in a double-space time transmit diversity (D-STTD) scheme.

According to the embodiment of the present invention, the most efficient transmission rate can be secured by more actively coping with the channel environment change, and the channel capacity can be increased within a limited frequency resource.

Hereinafter, a multi-input / output communication system and a control method thereof according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, in describing the embodiments of the present invention, when it is determined that detailed descriptions of related known functions or configurations may unnecessarily obscure the subject matter of the present invention, detailed descriptions thereof will be omitted.

According to an embodiment of the present invention, a multiple input / output communication system includes a plurality of modulation schemes according to MCS levels of an adaptive adaptive modulation and coding (AMC) scheme and a plurality of modulation schemes. Multiple coding rates are supported. The combination of coding rate and modulation scheme is called a Modulation and Coding Scheme (MCS), and a plurality of MCS levels may be defined from level 1 to level N according to the number of MCSs.

Table 1 below shows the MCS level configuration according to the high-speed downlink packet access (HSDPA) and 3G LTE standards.

TABLE 1

As shown in Table 1, MCS levels are assigned higher order modulation schemes and higher coding rates from MCS level 1 (QPSK, Turbocode 1/3) to MCS level 4 (64QAM, Turbocode 1/2). Can be set to The higher order modulation method and the coding rate have the advantage of better data rate than the lower order modulation method and the coding rate, and the lower order modulation method and the coding rate have the advantage of low error rate. Therefore, when the channel condition is good, a higher order modulation method and a higher coding rate (eg, MCS level 4) may be selected, and as the channel condition worsens, a lower order modulation method and a coding rate (eg, MCS level 1) may be selected. .

Here, the channel state may be estimated according to a signal to noise ratio (SNR), and it is possible to apply an MCS level corresponding to a preset SNR range. For example, it is possible to set MCS level 1 to be selected when the SNR range is -10 dB to -5 dB, and to set MCS level 4 when it is +10 dB or more. Criteria for setting the MCS level may be variously set according to each system.

1 is a control block diagram of a multiple input / output communication system according to an embodiment of the present invention.

As shown in FIG. 1, the embodiment of the present invention decodes a received signal by double-space time transmit diversity (D-STTD) to estimate a forward channel state, and a forward direction estimated by the receiver 200. The transmitter 100 selects the MCS level according to the channel state, codes and modulates transmission data of the forward channel according to the selected MCS level, and transmits a transmission symbol to each transmission antenna through D-STTD coding. Here, the receiver 200 may be located in a mobile terminal, and the transmitter 100 may be located in a base station.

The receiver 200 uses the D-STTD decoder 350 for decoding the received symbol received through the reception antenna Rx in the D-STTD scheme, and the S-channel (SNR) of the forward channel state by using the D-STTD decoded received symbol. a channel state estimator 240 for estimating signal to noise ratio, a demodulator 230 for demodulating a D-STTD decoded received symbol, and a channel deinterleaver 220 for channel deinterleaving the demodulated received bit data. And a decoder 210 for decoding the channel deinterleaved bit data and outputting the received data.

The transmitter 100 includes an MCS level selector 140 that selects an MCS level according to the forward channel state information estimated by the channel state estimator 240, and transmits data according to the MCS level selected by the MCS level selector 140. An encoder 110 for coding, a channel interleaver 120 for channel interleaving the coded transmission bit data according to the MCS level, a modulator 130 for modulating the channel interleaved transmission bit data according to the MCS level, D-STTD encoder 300 for D-STTD coding the modulated transmit symbol. Here, the MCS level selector 140 may be included in the transmitter 100 or may be included in the receiver 200, but the present embodiment describes a case in which the MCS level selector is included in the transmitter 100.

The modulator 130 and the demodulator 230 of the transmitter 100 and the receiver 200 may modulate and demodulate a signal using QPSK, 16QAM, and 64QAM modulation schemes.

The encoder 110, the channel interleaver 120, the decoder 210, and the channel deinterleaver 220 may perform channel coding and channel decoding using turbo coding methods having coding rates 1/3 and 1/2.

The channel state estimator 240 of the receiver 200 estimates the SNR, which is the state information of the forward channel, by using the received symbol demodulated by the D-STTD decoder 350. The channel state estimator 240 feeds back the SNR of the estimated forward channel to the transmitter 100.

The MCS level selector 140 of the transmitter 100 selects the MCS level according to the forward channel state fed back from the receiver 200. In accordance with the selected MCS level, encoder 110, channel interleaver 120, and modulator 130 channel code and modulate the transmission data. The modulated transmit data is coded in the D-STTD encoder 300 and transmitted to the transmit antenna. The MCS level selector 140 selects a higher order modulation method and a higher coding rate (eg, MCS level 4) when the channel condition is good, and as the channel condition worsens, the lower order modulation method and the coding rate (eg, MCS level 1). Can be selected.

With this configuration, the transmission data undergoes the channel coding and interleaving process selected by the MCS level selector 140 and then undergoes a modulation process according to the modulation technique selected by the MCS level selector 140 as well. The transmission symbol completed until the modulation process is encoded and transmitted through the D-STTD encoder 300. The signal passing through the channel is converted by the receiving end through the D-STTD decoder 350 to an estimated value of the original symbol. The estimated value of the received signal is restored to the original signal through the demodulator 230, the channel deinterleaver 220, and the decoder 210.

2 is a control block diagram of a D-STTD encoder 300 and a D-STTD decoder 350 of a multiple input / output communication system according to an exemplary embodiment of the present invention.

As shown in FIG. 2, the D-STTD technology is a method in which two STTDs are connected in parallel, and basically includes four transmitting antennas Tx and two receiving antennas Rx.

The D-STTD encoder 300 includes a demultiplexer 330 for multiplexing the modulated signal through the modulator 130 and a first STTD block 310 for encoding the modulated signal output from the demultiplexer 330 in a D-STTD manner. ) And the second STTD block 320.

The D-STTD decoder 350 includes a Zero Focusing (ZF) detector 340 which estimates a signal received by the receiving antenna Rx. The signal received by the D-STTD decoder 350 may be represented by the following <formula>.

<Formula>

Here, r represents a received signal, h represents a channel response, s represents a transmission signal, and n represents noise. In the case of a channel response, it is expressed in the form of h _ij , which means a channel response between the j th transmit antenna and the i th receive antenna. The channel response h _ij is independent and identically distributed (iid) and follows a complex Gaussian distribution with zero mean. Noise n is Additive White Gaussian Noise (AWGN) with an average of zero and a variance of σ ² I.

According to this configuration, the D-STTD encoder 300 encodes the transmitted symbols modulated by the modulator 130 through the first STTD block 310 and the second STTD block 320 to each of four modified signals. Transmit via the transmit antenna Tx. When transmitting in the D-STTD scheme, the transmission symbol streams S1, S2, S3, and S4 are divided into two symbol streams "S1, S2", "S3, S4" through the demultiplexer 330. The symbol streams "S1, S2" are encoded in the first STTD block 310, and the symbol streams "S3, S4" are encoded in the second STTD block 320. "S1, S2" encoded in the first STTD block 310 is transmitted through two antennas, and "S3, S4" encoded in the second STTD block 320 is also transmitted through two antennas. Therefore, both the multiplexing effect of transmitting data in parallel using the first STTD block 310 and the second STTD block 320 and the diversity effect of transmitting data through the two antennas can be obtained.

The D-STTD decoder 350 receives signals transmitted from four transmission antennas through two reception antennas. The D-STTD decoder 350 detects the received signal using a zero forcing (ZF) detector and outputs the estimated symbol stream to the demodulator 230. The ZF receiver 200 uses the channel matrix characteristic of the D-STTD system and detects the received signal by simply multiplying the inverse of the channel matrix in order to eliminate interference of signals from other transmitting antennas at the receiving end.

As a method for detecting a D-STTD signal, various algorithms such as a linear ZF algorithm, a minimum mean squared error (MMSE) algorithm, a nonlinear ZF algorithm, and a nonlinear MMSE algorithm are known. Accordingly, the ZF detector 340 may be modified in a form in which another algorithm is applied.

3 is a control flowchart of a multiple input / output communication system according to an embodiment of the present invention.

The channel state estimator 240 of the receiver 200 estimates the state of the forward channel by STTD decoding the signal received through the receiving antenna Rx (S100). Here, the channel state estimator 240 may estimate the SNR which is state information of the forward channel.

The channel state estimator 240 of the receiver 200 feeds back the estimated forward channel state to the transmitter 100 (S110).

The MCS level selector 140 of the transmitter 100 selects an MCS level according to the received channel information (S120). 4 is a graph illustrating a simulation result of MCS level selection probability of a multi-input / output communication system according to an exemplary embodiment of the present invention. The MCS level selection probability is represented by converting the MCS level selection probability into a total probability of 1 by applying the AMC and D-STTD 4 × 2 combining system in a Rayleigh flat fading environment. As shown in FIG. 4, when the SNR is low, the probability that MCS level 1 is selected is highest. That is, when the channel condition is not good, 1/3 turbo coding and QPSK modulation method having relatively low order modulation and low coding rate is used. On the other hand, when the SNR is high, the probability that MCS level 4 is selected is the highest. That is, when the channel condition is good, a half turbo coding and a 64QAM modulation scheme having a relatively higher order modulation and a higher coding rate are used.

The transmitter 100 codes and interleaves transmission data of a forward channel according to the selected MCS level (S130).

The transmitter 100 modulates transmission data of the forward channel according to the selected MCS level (S140).

The transmitter 100 encodes the modulated data in the D-STTD scheme (S150), and then transmits the modulated data in the D-STTD scheme through the transmission antenna (S160).

5 is a graph showing a result of simulating a transmission rate according to an MCS level. The graph of FIG. 5 shows the rate performance of a D-STTD 4 × 2 combining system in a Rayleigh Flat Fading environment.

When MCS level 1 (QPSK, turbo code 1/3) is applied, data is received without frame error at the maximum transmission rate with an SNR of about 2 dB or more, but when MCS level 4 (64QAM, turbo code 1/2) is applied When the SNR is about 18dB or more, it can be seen that the frame is transmitted without the frame error at the maximum transmission rate. That is, as in the prior art, assuming that only one specific channel coding rate and one specific modulation method should be selected, the coding rate or modulation method corresponding to MCS level 3 or 4 has a very high frame error probability in a low SNR period. It can be seen that there is no choice but to exclude the application.

Therefore, when the multi-input and output communication system according to the embodiment of the present invention is applied, and the MCS level is selected according to each SNR environment, it can be seen that data can be transmitted and received without a frame error in most SNR states.

FIG. 6 is a graph illustrating simulation results of a transmission rate performance of a conventional communication system and a multi-input / output communication system according to an exemplary embodiment of the present invention. It simulates the rate performance of the STTD 4x2 combining system and the conventional D-STTD 4x2 system.

As shown in FIG. 6, the maximum transmission rate of the AMC and D-STTD 4 × 2 combining system according to the embodiment of the present invention is about 10.9 Mbps, whereas the conventional D-STTD 4 × 2 system is about 2.7 Mbps. In addition, it can be seen that the maximum data rate is significantly higher.

In addition, it can be seen that the AMC and D-STTD 4 × 2 combining system according to the embodiment of the present invention exhibits even rate performance in all SNR intervals, compared to the conventional D-STTD 4 × 2 system.

As described above, the multi-input / output communication system according to the embodiment of the present invention selects the MCS level according to the SNR information. Therefore, the channel coding rate and the modulation method are flexibly applied according to the change of the channel response state, thereby ensuring the most efficient transmission rate in any SNR state.

Although the present invention has been described in detail with reference to exemplary embodiments above, those skilled in the art to which the present invention pertains can make various modifications to the above-described embodiments without departing from the scope of the present invention. Will understand. 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.

1 is a control block diagram of a multiple input / output communication system according to an embodiment of the present invention.

2 is a control block diagram of a D-STTD encoder and decoder in a multiple input / output communication system according to an embodiment of the present invention.

3 is a control flow diagram of a multi-input and output communication system according to an embodiment of the present invention.

4 is a graph showing a simulation result of MCS level selection probability of a multi-input / output communication system according to an exemplary embodiment of the present invention.

5 is a graph showing a simulation result of a data rate according to an MCS level of a multi-input / output communication system according to an exemplary embodiment of the present invention.

6 is a graph illustrating a simulation result of a transmission rate performance of a conventional communication system and a multiple input / output communication system according to various embodiments of the present disclosure.

Claims (20)

An MCS level selector for selecting a Modulation and Coding Scheme (MCS) level, which is a combination of data modulation and coding methods, in accordance with channel conditions; A modulation and coding unit for processing transmission data according to a modulation and coding method corresponding to the selected MCS level; And a D-STTD encoder for coding and transmitting the transmission data processed through the modulation and coding unit in a double-space time transmit diversity (D-STTD) scheme. The method of claim 1, And a channel state estimator for estimating a signal to noise ratio (SNR) of a received signal and providing the estimated SNR value to the MCS level selector. The method of claim 2, The MCS level selector, And selecting the MCS level according to the size of the SNR. The method of claim 3, The MCS level selector, And selecting the MCS level so that the coding rate of the coding scheme increases as the SNR of the channel increases. The method of claim 3, The MCS level selector, And selecting the MCS level so that the modulation order of the modulation scheme increases as the SNR of the channel increases. The method of claim 1, The modulation and coding unit, An encoder for coding the transmission data according to the selected MCS level; A channel interleaver for channel interleaving the coded data according to the selected MCS level; And a modulator for modulating the channel interleaved data according to the MCS level. The method of claim 6, The encoder, And coding the transmission data in one of 1/3 turbo coding and 1/2 turbo coding according to the selected MCS level. The method of claim 6, The modulator, And a multi-input / output communication system for modulating the transmission data by any one of QPSK, 16QAM, and 64QAM schemes according to the selected MCS level. The method of claim 1, The D-STTD encoder, A demultiplexer which multiplexes the transmission data processed through the modulation and coding unit; A first STTD block for encoding a part of a signal multiplexed by the demultiplexer according to a Space Time Transmit Diversity (STTD) scheme and transmitting the same to two antennas; And a second STTD block for encoding the remainder of the multiplexed signal in the demultiplexer using the STTD scheme and transmitting the same to two antennas. The method of claim 9, A first receiving antenna and a second receiving antenna for receiving data transmitted in the D-STTD scheme; A detector for detecting data received by the first antenna and the second antenna; And a D-STTD decoder for decoding the data detected through the detector in the D-STTD scheme. The method of claim 10, And a channel state estimator for estimating an SNR of a received signal received by either the first or second receiving antenna and providing the estimated SNR value to the MCS level selector. Selecting a Modulation and Coding Scheme (MCS) level, which is a combination of data modulation and coding methods, in accordance with the channel condition; Processing transmission data to a modulation and coding method corresponding to the selected MCS level; And coding and transmitting the modulated and coded transmission data in a Double-Space Time Transmit Diversity (D-STTD) scheme. The method of claim 12, Selecting the MCS level according to the channel state, Estimating a signal to noise ratio (SNR) of the received signal received through the channel; And selecting the MCS level according to the estimated SNR value. The method of claim 13, Selecting the MCS level according to the estimated SNR value, Selecting the MCS level such that the coding rate of the coding scheme increases as the SNR of the channel increases. The method of claim 13, Selecting the MCS level according to the estimated SNR value, And selecting the MCS level so that the modulation order of the modulation scheme increases as the SNR of the channel increases. The method of claim 12, The step of processing the transmission data to the modulation and coding method corresponding to the selected MCS level, And coding the transmission data in any one of 1/3 turbo coding and 1/2 turbo coding according to the selected MCS level. The method of claim 12, Modulating and coding the transmission data according to the selected MCS level, And modulating the transmission data according to any one of QPSK, 16QAM, and 64QAM schemes according to the selected MCS level. The method of claim 12, Coding and transmitting the modulated and coded transmission data in a double-space time transmit diversity (D-STTD) scheme, Multiplexing the modulated and coded transmission data into two streams; Encoding a part of the multiplexed signal by using a first space time transmit diversity (STSTD) scheme and transmitting the same to two antennas; Control method of input / output communication system. The method of claim 18, Receiving the data transmitted by the D-STTD scheme with a first receiving antenna and a second receiving antenna; Detecting data received by the first and second antennas; And decoding the detected data by the D-STTD method. The method of claim 19, Estimating an SNR of a received signal received by either the first or second receiving antenna; And selecting the MCS level according to the estimated SNR value.

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