KR20080105211A

KR20080105211A - Method and apparatus for space-time coding mode decision in mimo system, and method and apparatus for responding the decided stc mode

Info

Publication number: KR20080105211A
Application number: KR1020070052477A
Authority: KR
Inventors: 김병철; 이정자; 지상배
Original assignee: 포스데이타 주식회사
Priority date: 2007-05-30
Filing date: 2007-05-30
Publication date: 2008-12-04
Also published as: KR100910020B1; WO2008147107A1

Abstract

A method for deciding an STC(Space-Time Coding) mode in a MIMO(Multiple Input Multiple Output) system, and a method and an apparatus for responding to the decides STC mode are provided to determine an STC mode by considering an error which may occur when estimating a channel in the MIMO system. A device for deciding an STC mode includes: STC mode deciding unit; a channel parameter estimator which estimates channel gains and noise power from a signal received through plural receiving antennas; an STC SINR estimator(362) which estimates signal to interference and signal to ration by STC mode by using a channel gain and a noise power estimation value; and a channel capacity calculator(363) which calculates channel capacity by STC mode by suing the SINR estimation value.

Description

Method and Apparatus for Determining STC Mode in MIMO Wireless Communication System, Method and Apparatus for Determining StCT Mode {Method and Apparatus for Space-Time Coding Mode Decision in MIMO system, and Method and Apparatus for Responding the Decided STC Mode}

BRIEF DESCRIPTION OF THE DRAWINGS The figure explaining the outline | summary of a SISO system and a MIMO system.

2 is a block diagram illustrating a transmitter of an N × M MIMO system according to an embodiment of the present invention.

3 is a block diagram illustrating a receiver of an N × M MIMO system according to an embodiment of the present invention.

4 is a view for explaining the principle of transmission and reception of STTD in a 2 × 2 MIMO system.

5 is a view for explaining the principle of transmission and reception of the SM in a 2 × 2 MIMO system.

FIG. 6 is a configuration diagram illustrating a preferred STC mode determiner of FIG. 3. FIG.

7 is a flowchart illustrating a method for determining a preferred STC mode according to an embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

200: transmitter

210: encoder 220: interleaver

230: modulator 240: multiplexer and spatial encoder

250: Feedback message decoder 260: Scheduler

270: STC mode selector

300: receiver

310: demultiplexing and spatial decoding unit 320: demodulation unit

330: deinterleaver 340: decoder

350: MIMO channel parameter estimator 360: preferred STC mode determiner

The present invention relates to a multiple input multiple output (MIMO) wireless communication system, and more particularly, to a method and apparatus for determining an STC mode according to a given channel state in a receiver of a MIMO wireless communication system, and the determined STC mode. The present invention relates to a response method and an apparatus for responding to a transmitter.

In general, wireless channel environments inevitably introduce errors due to many factors such as multi-path interference, shadowing, propagation attenuation, time-varying noise, interference and fading, etc. This leads to loss of information. This loss of information causes severe distortion in the actual transmission signal, which causes a decrease in the overall performance of the wireless communication system.

Meanwhile, a diversity method is used to remove instability of communication due to fading. It is possible to increase the reliability of the communication link through diversity gain without increasing the bandwidth by equipping the transceiver with multiple antennas to secure additional space for resource utilization, and to increase the transmission capacity through parallel transmission through spatial multiplexing. You can also increase it.

1 is a view for explaining an outline of a SISO system and a MIMO system.

As shown in FIG. 1A, a single input single output (SISO) system performs a single input / output transmission through one channel H formed between one transmit antenna TxAnt and one receive antenna RxAnt. As a technology to perform, when a transmitting side and a receiving side each communicate with one antenna in a wireless communication, a multipath phenomenon occurs due to obstacles in a propagation path such as a hill or a steel tower, causing a problem due to fading. In communication, it causes a decrease in data rate and an increase in errors.

In contrast, a multiple input multiple output (MIMO) system transmits data through multiple paths by increasing the number of antennas of a base station and a terminal, reduces interference by detecting signals received on each path at the receiving end, and reduces space-time at the transmitting end. Diversity and spatial multiplexing can improve transmission efficiency. FIG. 1 (b) illustrates a 2 × 2 MIMO system using two transmit antennas and two receive antennas, of which a first and second transmit antennas TxAnt1 and TxAnt2 and a first are shown. Four channels, that is, a first channel H11, a second channel H12, a third channel H21, and a fourth channel H22 are formed between the second reception antennas RxAnt1 and RxAnt2.

In the case of the MIMO mode, a space time transmit diversity (STTD) and a spatial multiplexing (SM) mode may be classified according to a method of allocating a plurality of antennas and symbols to be transmitted, and in particular, IEEE In the 802.16d / e-based portable Internet system, STTD and SM are specified to be selectively transmitted. Therefore, a method of selecting such a space time coding (STC) mode according to channel conditions is under development.

In particular, when the STC mode is selected by considering only the very fundamental channel characteristics (for example, the variation of the MIMO channel strength and the MIMO channel strength) regarding the channel state, the influence of the error due to the channel estimation is ignored and performance degradation occurs. Since the decoding schemes vary depending on the STC mode and the characteristics thereof are different from each other, there is a problem in that the implemented results do not show ideal characteristics.

The present invention was devised to solve the above problems, and an object of the present invention is to provide a method and apparatus for determining a space-time coding (STC) mode in consideration of errors that may occur in channel estimation in a multi-input / output system. To provide.

Another object of the present invention is to provide a method and apparatus for determining a space-time coding (STC) mode in which characteristics of the STC mode decoding scheme are reflected in a multi-input / output system.

It is still another object of the present invention to provide a more practical STC through parameters reflecting characteristics of the STC mode decoding method and considering errors that may occur when a transmitter and a receiver are closed loop multiple input / output structures in a multiple input / output system. To determine a (Space-Time Coding) mode, and to provide a method and apparatus for responding to the signal transmitted from the transmitter by feeding back the determined STC mode.

For this purpose, a method of determining a space-time coding (STC) mode in a receiver of a MIMO system of one embodiment of the present invention includes (a) channel capacity for each STC mode from received signals received through a plurality of receiving antennas. Estimating; And (b) determining the STC mode using the estimated channel capacity.

In addition, a method of responding to a transmitter with respect to received signals received through a plurality of reception antennas in a receiver of a MIMO system of one embodiment of the present invention may include (a) estimating space-time coding (STC) mode from the received signals. Determining the STC mode of the transmitter using the allocated channel capacity; And (b) transmitting the determined STC mode in a feedback message to the transmitter.

On the other hand, an apparatus for determining a space-time coding (STC) mode in a receiver of a MIMO system of one embodiment of the present invention includes a channel parameter for estimating each channel gain and noise power from a received signal received through a plurality of receive antennas. Estimator; An STC SINR estimator estimating a Signal to Interference and Noise Ratio (SINR) for each STC mode using the channel gain and noise power estimates; A channel capacity calculator for calculating channel capacity for each STC mode using the SINR estimate; And an STC mode determiner configured to determine the STC mode using the channel capacity calculated for each STC mode.

Further, an apparatus for responding to a transmitter with respect to received signals received through a plurality of reception antennas in a receiver of a MIMO system of one embodiment of the present invention includes a channel estimated for each space-time coding (STC) mode from the received signals. An STC mode determiner configured to determine an STC mode of the transmitter using a capacity; And a feedback message transmitter configured to transmit the determined STC mode in a feedback message to the transmitter.

On the other hand, in the MIMO system of one embodiment of the present invention, an apparatus for transmitting a transmission signal to the receiver based on a reception response from the receiver uses the channel capacity estimated for each of the reception response -space-time coding (STC) modes. Including the determined STC mode information; An STC mode selection unit for selecting the STC mode-Space-Time Transmit Diversity (STTD) or Spatial Multiplexing (SM) based on the received response; And a space-time encoder that encodes the transmission signal according to the selected STC mode.

In the MIMO system of one embodiment of the present invention, a method for transmitting a transmission signal to the receiver based on a reception response from a receiver includes: (a) calculating channel capacity estimated for each reception response space-time coding (STC) mode; Including STC mode information determined using; (b) selecting the STC mode-Space-Time Transmit Diversity (STTD) or Spatial Multiplexing (SM) based on the received response; And (c) encoding the transmission signal according to the selected STC mode.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and preferred embodiments. For reference, in the following description, detailed descriptions of well-known functions and configurations that may unnecessarily obscure the subject matter of the present invention are omitted.

2 is a diagram illustrating a transmitter of an N × M MIMO system according to an embodiment of the present invention, and FIG. 3 is a diagram illustrating a receiver of an N × M MIMO system according to an embodiment of the present invention. As a base station (BS), a receiver may be referred to as a mobile station (MS), but this is merely an example, and it can be easily understood that the roles of the base station and the terminal for the transmitter or the receiver can be switched with each other. .

Referring to FIG. 2, the transmitter 200 includes an encoder 210, an interleaver 220, a modulator 230, a multiplexing and spatial encoder 240, a plurality of antennas, and a feedback message decoder. 250, a scheduler 260, and an STC mode selector 270. Referring to FIG. 3, the receiver 300 includes a plurality of antennas, a demultiplexer and a spatial decoder 310, and a multiplier. A grandfather 320, a deinterleaver 330, a decoder 340, a MIMO channel parameter estimator 350, and a preferred STC mode determiner 360 are included.

Hereinafter, for the convenience of explanation, the operation of the transmitter will be described first, followed by a brief description of the space-time coding (STC) related to the present invention, followed by the operation of the receiver.

In the transmitter 200, the encoder 210 outputs the encoded bit c _i by channel encoding the n th bit u _{n including the} information to be transmitted in a manner such as a forward error correction (FEC). For example, convolutional encoding, convolutional turbo codes (CTC), or the like is used as an encoding method. With respect to the encoded bits c _i, interleaver 220 re-arranged according to a predetermined rule to be transferred through the successive c _i of each channel have a low cross-correlation with a high correlation. For example, mapping to the non-adjacent sub-carriers with respect to a sequence c _i, or, may be in a constellation (constellation) with respect to a sequence c _i specify the rules described above to map to shift the lower or the upper bits. For the interleaved b _i , the modulator 230 maps one or more bits to one symbol using a modulation scheme such as QPSK or QAM. In addition, the multiplexing and spatial encoder 240 multiplexes the modulated symbols in a manner such as orthogonal frequency division multiplexing (OFDM) or code division multiplexing (CDM), and then, partially or entirely, all symbols according to the selected STC mode. A plurality of antennas may be used to transmit to the receiver 300.

At this time, the mapping between the symbol and the antenna is called space-time coding (STC), and is classified into space-time transmit diversity (STTD) and spatial multiplexing (SM) according to an encoding scheme. Can be.

STTD is a method of repeatedly transmitting two different symbols by repeatedly changing the phase of each symbol and an antenna to transmit each symbol, and an Alamouti method is typical. It guarantees stable and improved data rate. On the other hand, SM is a method of simultaneously transmitting and receiving a plurality of different symbols through a plurality of antennas, typically the BLAST method, and increases the data rate. In particular, in IEEE 802.16d / e-based portable Internet system, since STTD and SM are specified to be selectively transmitted, a technology for transmitting them after proper performance comparison is required.

Since the relative performance of the STTD and the SM is different depending on the channel state, as described above, these should be appropriately selected and used. To this end, the receiver 300 analyzes the channel characteristics from the signal transmitted from the transmitter 200, determines the STTD or SM according to a predetermined determination criterion, and encodes the information about the transmitted signal to the transmitter 200, that is, Feedback. In this case, the encoded information includes the STC mode and the effective CINR (CINR) determined by the receiver 300, and is transmitted to the transmitter 200 at a predetermined time.

Hereinafter, the information encoded and transmitted as described above is called a feedback message, and the STC mode determined by the receiver 300 is referred to as a preferred STC mode. The STTD and the SM will be described in more detail with reference to FIGS. 4 and 5 to be described later.

In FIG. 2, the feedback message decoder 250 decodes the information transmitted from the receiver 300 and provides it to the STC mode selector 270, and the scheduler 260 selects an STC mode such as a resource state and a scheduling strategy. To the unit 270. Accordingly, the STC mode selector 270 may finally determine the STC mode to be transmitted to the receiver 300 in consideration of the resource state and the scheduling strategy.

Meanwhile, in FIG. 3, the receiver 300 demultiplexes received signals from a plurality of antennas in symbol units and demultiplexes the spatial decoder 310 and performs ST decoding. In particular, when the STC mode is STTD, the decoding is performed using at least two symbol indices. When the STC mode is SM, the decoding is performed on each received symbol. The demodulator 320 demodulates the demultiplexed and decoded symbols to calculate a bit matrix. The deinterleaver 330 deinterleaves the inverse of the interleaving scheme applied by the transmitter 200, and the decoder 340 decodes the demultiplexed symbols. The information bit estimate originally transmitted by the transmitter 200 is output based on the deinterleaved bit string.

In addition, the receiver 300 uses the MIMO channel parameter estimator 350 that analyzes MIMO channel characteristics, such as MIMO channel estimation and noise power, from the signal transmitted from the transmitter 200, and uses the estimated MIMO channel and noise power. The apparatus may further include a preferred STC mode determiner 360 that determines a preferred STC mode, and the MIMO channel parameter estimator 350 may be included in the configuration of the preferred STC mode determiner 360.

Hereinafter, after describing the STC mode and the process of calculating the SINR for each STC mode with reference to FIGS. 4 and 5, the apparatus for determining an STC mode according to an embodiment of the present invention will be described with reference to FIGS. 6 and 7. The method will be described.

4 is a view for explaining the principle of transmission and reception of the STTD in a 2 × 2 MIMO system.

Referring to FIG. 4, if two transmission symbols (or sub-symbols of OFDMA) are s ₁ and s ₂ , respectively, and each row can be represented by a vector corresponding to each antenna, k and k + The first transmission symbol vectors s (k) and s (k + 1) may be represented by Equation 1 below. Here, k is assumed to be an even number among the STTD symbol indices, and k = 0, 2, 4,...

[Equation 1]

When the transmission symbol vectors s (k), s (k + 1), s (k + 2), ... are transmitted from the antenna of the transmitter 200, they are received by the antenna of the receiver 300. The received sample vectors r (k), r (k + 1), r (k + 2), ... are obtained from the signal. Here, the channel gain between the n (n = 1,2) th antenna of the transmitter 200 and the m (m = 1,2) th antenna of the receiver 200 is h _n _{, m} and reception of the m th reception antenna is performed. If the noise component of the k-th received sample from the signal is v _m (k), the received sample vector may be represented by Equation 2 below.

[Equation 2]

In the case of STTD, STC decoding recovering the symbols s _k and s _k ₊ ₁ transmitted from the transmitter 200 from the received sample vectors r (k) and r (k + 1) is relatively simple and can be performed with one antenna. In addition, when two antennas (2 × 2) are used, the reception diversity gain may be further obtained. Therefore, when the noise power in the m-th antenna of the receiver 300 is σ _m ² , the recovered symbols S _k and S _k ₊ ₁ may be represented by Equation 3 below.

[Equation 3]

If at least one of four channel gains h _n _{, m} is not 0 in Equation 3, the recovered symbols S _k and S _k ₊ ₁ can be obtained. Here, the symbol energy transmitted from the transmitter 200 is referred to as E _s / N = 1/2, and the noise components are spatially (different antennas), temporal (different temporal indexes), and are not correlated with each other. ), The signal-to-noise ratio (SNR _STTD ) of the estimated symbols can be expressed by Equation 4 below.

[Equation 4]

Meanwhile, FIG. 5 is a diagram for explaining a transmission / reception principle of an SM in a 2 × 2 MIMO system. Referring to FIG. 5, in the SM, all transmission symbol vectors are independent of time index k. Therefore, unlike decoded from the received sample vectors of two consecutive received signals of r (k) and r (k + 1) for s (k) in the above-described STTD, s (k) is equal to r (k) in SM. It must be decrypted with bay.

The optimal decoding method in SM is known as Maximum Likelihood Decoding (MLD), and zero-forcing (ZF) and minimum mean squared error (MMSE) are presented. In the present embodiment, an SM decoding method using the MMSE method will be described as an example.

In the MMSE SM decoding method, a symbol s _k and s _k ₊ ₁ transmitted from the transmitter 200 are estimated by linearly combining received samples obtained from each antenna. If this is expressed as an expression, it may be expressed as Equation 5 below. Here, the superscript " ^H " means a matrix transpose conjugate.

[Equation 5]

Accordingly, in the MMSE type STC decoding, after decoding the symbol transmitted from the nth transmission antenna, the SINR for the symbol may be expressed as in Equation 6 or Equation 7 below. Here, Equation 7 is expressed by Equation 6

Equation 6 and Equation 7 R _rr is

Is a correlation matrix for a received sample vector, where H is a channel matrix and h _n = [h _n _{, 1} , ..., h _n _{, M} ] ^T. In addition, I _N is an N × N identity matrix.

[Equation 6]

[Equation 7]

As a result, referring to Equations 4 and 6 (or Equation 7) described above, SINR after decoding of STTD and SINR after decoding of SM (that is, STTD post SINR and SM post SINR) are channel gains h _{n, m} In addition, it can be seen that it also depends on the decoding method according to the STC mode and STC mode. Thus, it can be seen that the preferred STC mode determined by the receiver 300 cannot be determined simply by channel characteristics. Therefore, in the present embodiment, the preferred STC mode may be determined by considering a decoding method according to the STC mode and deriving a comparable parameter from SINRs after decoding of the STTD or SM. For example, if the preferred STC mode is determined using the channel capacity, the preferred STC mode suitable for a given channel situation can be selected, thereby maximizing transmission efficiency.

FIG. 6 is a block diagram showing the preferred STC mode determiner of FIG. 3. The preferred STC mode determiner 360 does not determine the STC mode based on the exact channel characteristics, but estimates the channel characteristics and obtains the estimated channel characteristics. After obtaining the Post Signal to Interference and Noise Ratio (STSI) for each STC mode, the preferred STC mode is determined based on the channel capacity obtained using the post SINR for each STC mode. By doing so, most errors due to the actual implementation and characteristics of the decoding scheme are considered, and thus data can be detected more accurately. Here, post SINR means SINR after decoding for each STC mode.

Referring to FIG. 6, the preferred STC mode determiner 360 estimates the STC post SINR from the channel and noise power estimate estimated by the MIMO channel parameter estimator 350 of FIG. 3. And a channel capacity calculating module 363 that calculates channel capacity for each STC using a mathematical formula or a previously prepared reference table from the above-described post SINR estimate, and a cumulative average for calculating a difference between channel capacity for each STC mode. An average operation module 364 and an STC mode determination module 365 for determining a preferred STC with reference to the cumulative average value. Here, the STC post SINR estimation module 362 includes an STTD post SINR estimation module 362a for estimating SINR after STTD decoding and an SM post SINR estimation module 362b for estimating SINR after SM decoding, and a channel capacity calculation module 363 includes an STTD channel capacity calculation module 363a and an SM channel capacity calculation module 363b.

The STC post SINR estimation module 362 estimates the STC post SINR from the channel and noise power estimate estimated by the MIMO channel parameter estimator 350. The STC post SINR estimation module 362 is expressed in k-th processing unit for the l- th frame in the OFDM or OFDMA mode, and estimates the entirety of the 1- th frame using the representative value from the k-th processing unit. The SINR estimation module 362 includes an STTD post SINR estimation module 362a for estimating SINR after STTD decoding and an SM post SINR estimation module 362b for estimating SINR after SM decoding according to a method of allocating the processing unit to a transmission antenna. Separated by).

The channel capacity calculating module 363 calculates the channel capacity for each STC mode from the above-described post SINR estimation value by using an equation or a previously prepared reference table. For example, in the case of using the equation, the channel capacity for each STC mode is calculated by using the channel capacity of Shannon, and in the case of using the reference table, the channel capacity according to the above-described post SINR estimate is stored in advance, and the channel capacity according to the specific post SINR estimate is stored. Read from a lookup table. The channel capacity calculation module 363 is divided into an STTD channel capacity calculation module 363a and an SM channel capacity calculation module 363b according to a method of allocating the processing unit to a transmission antenna.

The cumulative average calculation module 364 calculates a cumulative average for the difference in channel capacity for each STC mode. For example, the difference between the SM channel capacities is calculated from the STTD channel capacities every frame, and then accumulated. In this case, it should be noted that the SM channel capacity is accumulated according to the number of transmission antennas in the frame of the received signal received from the nth transmission antenna.

The STC mode determination module 365 determines the preferred STC by referring to the cumulative average value described above. For example, as described above, the cumulative average value is obtained from the difference of the SM channel capacity from the STTD channel capacity or the difference of the STTD channel capacity from the SM channel capacity, and the preferred STC mode is determined according to whether the cumulative average value is positive or negative.

Although not shown in FIG. 6, when the transmitter 200 and the receiver 300 have a closed loop MIMO structure, the receiver 300 transmits the determined preferred STC mode to a feedback message and transmits the feedback message to the transmitter. It may further include a transmitter (not shown) to be used as a response device to the signal transmitted from the transmitter 200.

A method of determining an STC mode according to an embodiment of the present invention configured as described above will be described in detail with reference to FIG. 7.

For each subcarrier unit or frequency-time (subcarrier-OFDMA symbol), the signal received from each antenna is properly processed in the RF section (not shown), quantized to form a baseband OFDMA symbol frame, and for each preset subcarrier sample population. Adjacent subcarriers in the 2D region may be clustered and processed into a cluster of a certain size. In addition, this subcarrier sample population may be all or part of an OFDMA symbol using STC in a corresponding frame. Therefore, hereinafter, an index for a unit (subcarrier or cluster) processed in one frame is referred to as k, and an index for the frame is referred to as l .

First, channel gain and noise power, which are parameters required for estimating post SINR, are estimated (S710). In this case, channel gain and noise power are estimated for each processing unit (eg, subcarrier or cluster) for each frame. In this case, a pilot may be used to estimate the channel gain, and in this case, an interpolation method or an average method using a pilot may be applied.

Subsequently, the post SINR for each STC mode is estimated from the channel and noise power estimates (S720).

For STTD, the STTD post SINR corresponding to the sample population of the l th frame from the channel gain and noise power estimates.

Estimate For example, in the OFDM or OFDMA scheme, since a plurality of subcarriers are used, a multipath channel is considered. In this case, both channel characteristics and noise power including interference may have different values depending on the aforementioned processing units (subcarriers or clusters). It can be expressed as Equation 8. Where h _n _{, m} ( l , k) represents the channel gain for the k-th processing unit of the l- th frame, and σ _m ² ( l , k) represents the l- th frame received by the m-th antenna of the receiver 300. Interference and noise power for the k th processing unit of.

[Equation 8]

In addition, the method for setting the STTD post SINR representative value for the entire l- th frame may use one of a geometric mean, an arithmetic mean, or a median value for the index k. Here, the geometric mean may be represented by Equation 9, the arithmetic mean by Equation 10, and the median by Equation 11, where median <x ( l , k) | l > is given by l when x is given. Median for ( l , k).

[Equation 9]

[Equation 10]

[Equation 11]

Meanwhile, in the case of SM, the SM post SINR for a frame transmitted from the nth transmission antenna of the transmitter 200 according to Equation 6 or 7 from the channel gain and noise power estimate.

Can be obtained. For example, in the OFDM or OFDMA scheme, since a plurality of subcarriers are used, a multipath channel is considered. In this case, since the channel characteristics and the noise power including interference may have different values according to the above-described processing units, they are transmitted from the nth transmission antenna. SM SINRNR in the kth processing unit of the l th frame.

May be represented by Equation 12 or Equation 13. Here, the above-mentioned processing unit represents a subcarrier or a cluster.

[Equation 12]

[Equation 13]

In addition, the method of setting the SM post SINR representative value for the entire l- th frame of the nth transmission antenna may use one of a geometric mean, an arithmetic mean, or a median value for the index k. Here, the geometric mean may be represented by Equation 14, the arithmetic mean by Equation 15, and the median value by Equation 16. In Equation 16, median <x ( l , k) | l> is the median value for x (l, k) when l is given.

[Equation 14]

[Equation 15]

[Equation 16]

Next, the channel capacity for each STC mode is calculated from the above-described post SINR estimation value for each STC mode using an equation or a reference table prepared in advance (S730). For example, in the case of using the equation, the channel capacity of the STTD is obtained from the following equation (17), and the channel capacity of the SM is obtained from the following equation (18). In Equation 18, the cumulative channel capacity for N transmission antennas in the SM is represented.

[Equation 17]

Equation 18

This channel capacity is basically derived from Equations 19 and 20 below. That is, in the wireless channel, the frequency efficiency is defined as the data rate per unit frequency, and when the unit is bps / Hz, the frequency efficiency that can be transmitted without error is defined by the channel capacity of Shannon. In the case of the SISO system having one transmit and receive antenna, the channel capacity of Shannon may be expressed as in Equation 19 below. Where p is the SNR.

[Equation 19]

C = log ₂ (1 + ρ)

If Shannon's channel capacity is applied to a transmission / reception system using multiple antennas (particularly in a 2 × 2 MIMO system), that is, a MIMO system, the channel capacity may be expressed by Equation 20 below.

[Equation 20]

C = log ₂ (Det (I + ρHH ^H / 2))

On the other hand, in the case of using the reference table, the channel capacity for each MCS level related to the channel characteristics is created in advance in the table, and the table can be referred to whenever the preferred STC mode is determined.

Next, a cumulative average is calculated with respect to the difference in channel capacity for each STC (S740). That is, the difference in the channel capacity for each STC mode for each frame is cumulatively averaged as in Equation 23 using Equation 21 or 22 below. Where α ( l ) is

At the time of calculation

Is a variable to control the contribution rate.

[Equation 21]

[Equation 22]

[Equation 23]

The preferred STC mode is determined with reference to the cumulative average value described above (S750). That is, the STC mode is determined according to whether the cumulative average value is positive or negative. For example, in the process of calculating the cumulative average value, using the above-described Equation 21,

Select SM when> 0,

Select STTD when ≤ 0. However, in the process of calculating the cumulative average value, the equation (22) described above is used.

When S≥D, select STTD,

Select SM when <0.

By doing so, as described above, when the preferred STC mode is determined using the channel capacity, the preferred STC mode suitable for a given channel situation can be selected, thereby maximizing transmission efficiency.

Although not shown in FIG. 7, when the transmitter 200 and the receiver 300 have a closed loop MIMO structure, the receiver 300 transmits the determined preferred STC mode to a feedback message to the transmitter ( Not shown) may be used as a response method for the signal transmitted from the transmitter 200.

Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art to which the present invention pertains can implement the present invention in other specific forms without changing the technical spirit or essential features, The examples are to be understood in all respects as illustrative and not restrictive. For example, in the present embodiment, for the sake of convenience of explanation, the description will be mainly focused on a 2 × 2 MIMO system, but it can be seen that the present invention is applicable to an N × M MIMO system (M ≧ N).

In addition, the scope of the present invention is specified by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts are included in the scope of the present invention. Should be interpreted as

According to the present invention, by determining a preferred space-time coding (STC) mode in consideration of an error that may occur in channel estimation in a multi-input and output system, it is possible to determine the STC mode suitable for the channel situation to maximize the transmission efficiency There is.

In addition, according to the present invention, by determining the preferred space-time coding (STC) mode reflecting the characteristics of the decoding scheme for each STC mode in the multi-input output system, there is an effect that can be determined more accurately.

In addition, according to the present invention, when a transmitter and a receiver are closed loop multi-input / output structures in a multi-input / output system, the error that may occur in channel estimation is considered, and the preferred space-time coding (STC) mode reflected in the decoding method for each STC mode. By deciding and feeding it back to the transmitter, the transmitter can determine the STC mode in which more substantial and accurate channel characteristics are considered in the next frame transmission.

Claims

A method of determining a space-time coding (STC) mode in a receiver of a MIMO system,

(a) estimating channel capacity for each STC mode from received signals received through a plurality of receiving antennas; And

(b) determining the STC mode using the estimated channel capacity.

The method of claim 1, wherein the STC mode,

STC mode determination method comprising space-time transmit diversity (STTD) and spatial multiplexing (SM).

The method of claim 1, wherein the channel capacity,

STC mode determination method characterized in that it is obtained by using the signal-to-interference and noise ratio based on the received signal.

The method of claim 1, wherein step (a) comprises:

(a-1) estimating each channel gain and noise power from the received signal;

(a-2) estimating signal to interference and noise ratio (SINR) for each STC mode using the channel gain and noise power; And

(a-3) calculating a channel capacity for each STC mode using the estimated SINR.

The method according to any one of claims 1 to 4, wherein step (b) comprises:

(b-1) calculating a cumulative average of the difference of the channel capacity for each STC mode; And

(b-2) determining the STC mode using the cumulative average value.

The method according to any one of claims 1 to 4, wherein the channel capacity,

If the receiver supports OFDM or OFDMA, STC mode determination method, characterized in that estimated in sub-carrier or cluster unit.

A method of responding to a transmitter with respect to received signals received through a plurality of receiving antennas at a receiver of a MIMO system,

(a) determining the STC mode of the transmitter using the channel capacity estimated for each space-time coding (STC) mode from the received signal; And

and (b) transmitting the determined STC mode in a feedback message to the transmitter.

The method of claim 7, wherein the feedback message,

And further including an effective CINR of the receiver and transmitted to the transmitter at a specific time.

The method of claim 7, wherein the STC mode,

A response method comprising space-time transmit diversity (STTD) and spatial multiplexing (SM).

The method according to any one of claims 7 to 9, wherein the channel capacity,

And obtaining the signal using the signal-to-interference and noise ratio based on the received signal.

The method according to any one of claims 7 to 9, wherein step (a) comprises:

(a-1) estimating each channel gain and noise power from the received signal;

(a-2) estimating signal to interference and noise ratio (SINR) for each STC mode using the channel gain and noise power;

(a-3) calculating channel capacity for each STC mode using the estimated SINR; And

(a-4) determining the STC mode using the channel capacity calculated for each STC mode.

The method according to any one of claims 7 to 9, wherein the channel capacity,

If the receiver supports OFDM or OFDMA, the response method characterized in that it is estimated in subcarriers or cluster units.

An apparatus for determining a space-time coding (STC) mode in a receiver of a MIMO system,

A channel parameter estimator for estimating each channel gain and noise power from the received signals received through the plurality of receiving antennas;

An STC SINR estimator estimating a Signal to Interference and Noise Ratio (SINR) for each STC mode using the channel gain and noise power estimates;

A channel capacity calculator for calculating channel capacity for each STC mode using the SINR estimate; And

And an STC mode determiner configured to determine the STC mode by using the channel capacity calculated for each STC mode.

The method of claim 13,

And a cumulative average calculating unit configured to calculate a cumulative average with respect to the difference in channel capacity for each STC mode.

The method of claim 13, wherein the channel parameter estimator,

And estimating the channel gain and the noise power in each processing unit of the received signals.

The method of claim 15, wherein the processing unit,

STC mode determination apparatus, if the receiver supports OFDM or OFDMA, it is a subcarrier or a cluster.

The method of claim 13, wherein the STC SINR estimator,

A STTD SINR estimation module for estimating STTD SINR after decoding the received signal with space-time transmit diversity (STTD); And

And an SM SINR estimation module for estimating SM SINR after spatially multiplexing the received signal.

The method of claim 17, wherein the STTD SINR estimation module,

And a representative value for a specific frame of the received signal using one of a geometric mean, an arithmetic mean, or a median value for the STTD SINR.

The method of claim 17, wherein the SM SINR estimation module,

And a representative value for a specific frame of the received signal using one of a geometric mean, an arithmetic mean, or a median value for the SM SINR.

The method of claim 17, wherein the channel capacity calculation unit,

An STTD channel capacity calculation module for calculating channel capacity of the STTD from the STTD SINR estimate; And

And an SM channel capacity calculating module for calculating a channel capacity of the SM from the SM SINR estimate.

The method of claim 17, wherein the STC mode determiner,

And determining the STC mode according to whether the cumulative average value of the channel capacity difference of the STTD and the channel capacity difference of the SM is positive or negative.

An apparatus for responding to a transmitter for received signals received through a plurality of receiving antennas at a receiver of a MIMO system,

An STC mode determiner configured to determine an STC mode of the transmitter using the channel capacity estimated for each space-time coding (STC) mode from the received signal; And

And a feedback message transmitter configured to transmit the determined STC mode in a feedback message to the transmitter.

The method of claim 22, wherein the feedback message is

And an effective CINR (Effective CINR) of the receiver, wherein the response device is transmitted to the transmitter at a specific time.

The method of claim 22, wherein the STC mode,

A response device comprising Space-Time Transmit Diversity (STTD) and Spatial Multiplexing (SM).

The method according to any one of claims 22 to 24, wherein the STC mode determination unit,

And when the receiver supports OFDM or OFDMA, estimating the channel capacity from the received signal in subcarriers or cluster units.

A channel parameter estimation module for estimating each channel gain and noise power from the received signal;

An STC SINR estimation module for estimating signal to interference and noise ratio (SINR) for each STC mode by using the estimated channel gain and noise power estimate;

A channel capacity calculation module for calculating channel capacity for each STC mode using the SINR estimate; And

And an STC mode determination module for determining an STC mode using the channel capacity.

An apparatus for transmitting a transmission signal to the receiver based on a reception response from a receiver in a MIMO system,

A feedback message decoder which decodes the reception response, including STC mode information determined by using channel capacity estimated for each space-time coding (STC) mode;

An STC mode selection unit for selecting the STC mode-Space-Time Transmit Diversity (STTD) or Spatial Multiplexing (SM) based on the received response; And

And a space-time encoder that encodes the transmission signal according to the selected STC mode.

A method for transmitting a transmission signal to the receiver based on a reception response from a receiver in a MIMO system,

(a) decoding the reception response, including STC mode information determined using channel capacity estimated for each space-time coding (STC) mode;

(b) selecting the STC mode-Space-Time Transmit Diversity (STTD) or Spatial Multiplexing (SM) based on the received response; And

(c) encoding the transmission signal according to the selected STC mode.