CN101232356A

CN101232356A - Precoding method, system and apparatus in MIMO system

Info

Publication number: CN101232356A
Application number: CNA2007100730377A
Authority: CN
Inventors: 文雪; 李�杰; 王吉滨
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2007-01-24
Filing date: 2007-01-24
Publication date: 2008-07-30

Abstract

The invention discloses a pre-coding method, a system and a device in a MIMO system. The method, the system and the device which are related to by the invention can be applied in the orthogonal space-time coding circumstance. The inventive method adopts a non-unitary matrix for pre-coding, and the non-unitary matrix is obtained by judging the obtained optimal pre-coding vector construction. The inventive system includes a transmitter and a receiver, wherein, the transmitter includes a code list, a pre-coding matrix construction unit and a pre-coding unit; the receiver includes a channel estimation unit, the code list and a judgement unit. The simulation and the analysis show that, compared with the prior art, the usage of the inventive proposal can lower the bit error rate and reduce the complexity of decoding simultaneously in the situation of the same signal-to-noise ratio.

Description

Precoding method, system and device in MIMO system

Technical Field

The present invention relates to wireless communication technologies, and in particular, to a precoding technology in a MIMO system.

Background

Information theory research proves that a communication system adopting Multiple antennas can obtain higher channel capacity, under the assumption that channels are independent Rayleigh fading and a receiver knows channel state information, the theoretical channel capacity of a Multiple Input Multiple Output (MIMO) system adopting Multiple antennas at a transmitting end and a receiving end is approximately linearly increased along with the smaller value of the number of transmitting antennas and the number of receiving antennas, and the mode of improving the capacity of the MIMO system is called space division multiplexing. The MIMO-OFDM system, in which the MIMO system is combined with an Orthogonal Frequency Division Multiplexing (OFDM) technology, can effectively combat multipath fading of a wireless channel, and is recognized as the most competitive technology for fourth-generation mobile communication.

MIMO can exploit multiple independent channel gains to combat wireless channel fading, referred to as diversity, including space diversity, time diversity, and frequency diversity. The Space division multiplexing and the Time diversity are combined by a Vertical layered Space-Time Codes (V-BLAST) structure and Orthogonal Space-Time Block Codes (OSTBC), and both the two coding modes belong to Space-Time coding schemes.

Generally, a transmitting end of a MIMO system does not know channel state information, however, if the transmitting end can know the channel state information, we can perform certain processing on a transmitting Signal at the transmitting end, reduce interference, and improve an average received Signal-to-Noise Ratio (SNR), thereby reducing an average symbol error rate, which we call this processing of the transmitting end as precoding. The channel state information required by the transmitting end may be instantaneous channel estimation, or first-order or second-order statistical information of the channel estimation, which depends on the time fading characteristics of the channel, for example, for a fast fading system, we generally adopt the statistical characteristics of the channel estimation to reflect the channel information; for slow fading systems, we generally use instantaneous channel estimation.

In a symmetric Time Division Duplex (TDD) system, channel information of uplink and downlink channels can be shared with each other, and in this case, precoding can be applied to both the base station and the mobile station without any change to the system structure. However, for an asymmetric time Division Duplex (tdd) system or a Frequency Division Duplex (FDD) system, the situation is completely different, taking downlink precoding of such a system as an example, due to asymmetry of uplink and downlink channels, a receiving end needs to transmit channel information to a transmitting end through a feedback channel to enable the receiving end to know the downlink channel, so we call the MIMO system using the feedback mechanism to be a Closed-loop MIMO (CL-MIMO) system, and correspondingly, the MIMO system without feedback is an Open-loop MIMO (OP-MIMO) system. The closed-loop MIMO system can optimize the system performance through feedback, and better exert the advantage of MIMO, and thus becomes one of the hot spots of recent MIMO research.

However, the channel information increases with the product of the number of transmit antennas, the number of receive antennas, and the number of users, and for the MIMO channel capacity linearly increasing with the number of transmit antennas or the number of receive antennas, it is difficult to achieve complete channel information (ideal feedback) to be fed back in a practical system. A limited feedback precoding scheme can solve the above-mentioned problems. A closed loop MIMO system adopting limited feedback precoding stores a group of precoding matrixes called codebooks at the two ends of a receiving end and a transmitting end in advance. At the receivingThe end system selects an optimal precoding matrix from the codebook according to channel estimation and a certain judgment criterion, the index of the optimal precoding matrix is fed back to the sending end, and the sending end obtains the precoding matrix according to the index. Taking a codebook containing N precoding matrices as an example, the limited feedback precoding scheme only needs to feed back log₂N bits can obtain a precoding matrix, and the feedback information amount is greatly reduced. It can be said that the limited feedback precoding is a quantization of the ideal precoding matrix space.

At present, most of precoding research documents and ieee802.16e protocol standard draft adopt the above precoding scheme, and the physical layer of ieee802.16e combines the precoding scheme with three space-time coding schemes, namely Beam Forming (BF), vertical layered space-time coding and orthogonal space-time block coding.

The structure and the work flow of a limited feedback precoding MIMO-OFDM system are shown in figure 1.

At a transmitting end, firstly, data to be transmitted is modulated to generate modulated symbols, then space-time mapping (namely space-time coding) is carried out on the modulated symbols, signals obtained by the space-time mapping are pre-coded, finally, the signals are transmitted out through an antenna after fast Fourier inverse transformation, D \ A transformation and up-mixing. In the precoding stage, the sending end receives feedback information sent by the receiving end through a feedback channel, and the information informs the sending end which precoding matrix should be selected for precoding. And after receiving the information, the sending end selects the precoding matrix in the codebook set and performs precoding on the signals obtained by space-time mapping by adopting the matrix.

At a receiving end, after an antenna receives a signal, on one hand, the signal is subjected to down-mixing, A \ D conversion and fast Fourier conversion, the converted signal is used as one of input signals of a decoder, on the other hand, the receiving end selects an optimal precoding matrix from a codebook according to channel estimation and an optimal decision criterion, the serial number of the optimal precoding matrix is fed back to a transmitting end through a feedback channel, and meanwhile, the last optimal precoding matrix and the channel estimation are sent to the decoder for decoding. The specific decision process is as follows: and the receiving terminal equipment carries out channel estimation according to the received signal, utilizes the channel condition information obtained by the channel estimation and combines each pre-coding matrix in the codebook set to carry out optimal judgment, and sends the judgment result to the sending terminal through a feedback channel.

The key to the limited feedback precoding is the codebook and the optimal decision criterion, which will directly affect the bit error rate performance of the system. The optimal precoding matrix obtained through judgment is F, and the draft of the IEEE802.16e protocol considers that precoding does not increase the total transmitting power according to the precoding theory, namely the requirement of precoding is met

<math><mrow> <munder> <mi>max</mi> <mrow> <mi>s</mi> <mo>&Element;</mo> <msup> <mi>S</mi> <msub> <mi>M</mi> <mi>s</mi> </msub> </msup> </mrow> </munder> <mfrac> <msub> <mrow> <mo>|</mo> <mo>|</mo> <mi>Fs</mi> <mo>|</mo> <mo>|</mo> </mrow> <mn>2</mn> </msub> <msub> <mrow> <mo>|</mo> <mo>|</mo> <mi>s</mi> <mo>|</mo> <mo>|</mo> </mrow> <mn>2</mn> </msub> </mfrac> <mo>≤</mo> <mn>1</mn> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow></math>

Wherein S represents a set of transmit signal vectors, S represents a set of modulation symbols, | |₂The expression takes the vector 2 norm. Since the unitary matrix has the property of not changing the vector norm, a unitary matrix (when the number of transmit antennas is equal to the number of data streams) or a pseudo-unitary matrix (when the number of transmit antennas is greater than the number of streams) is often used as a precoding matrix in precoding.

The ieee802.16e protocol draft is also unitary matrix precoding employed. Therefore, the precoding matrix F specified in the protocol draft is a unitary matrix (when the number of transmit antennas is equal to the number of data streams) or a pseudo-unitary matrix (when the number of transmit antennas is greater than the number of streams).

In addition, the codebook is classified according to different numbers of transmitting antennas, different numbers of data streams and different configurations of feedback bits, a method for classifying the codebook is also provided in the draft of the ieee802.16e protocol, a codebook configured according to different numbers of transmitting antennas, different numbers of data streams and different configurations of feedback bits is defined, an available codebook given in the draft is detailed in table 1, and "-" indicates that the codebook is not specified in the protocol.

Table 1ieee802.16e protocol codebook

Therefore, after the receiving end receives the signal, one of the codebooks shown in table 1 is selected for optimal decision according to the number of transmitting antennas, the number of data streams and the number of feedback bits.

Taking the Alamouti orthogonal space-time block coding received by the closed-loop 2 transmitter 1 as an example, if the feedback bit number is 3 bits, the optimal precoding matrix F is selected from the (2, 2, 3) codebook set in table 1; if the number of feedback bits is 6 bits, F is selected from the (2, 2, 6) codebook set in table 1.

The purpose of the optimal decision is to minimize the error rate or maximize the capacity, which is different according to the decoding algorithm, and the specific expression of the optimal decision criterion for minimizing the error rate is

<math><mrow> <mi>F</mi> <mo>=</mo> <munder> <mrow> <mi>arg</mi> <mi>max</mi> </mrow> <mrow> <msub> <mi>F</mi> <mi>i</mi> </msub> <mo>&Element;</mo> <mi>Φ</mi> </mrow> </munder> <msub> <mrow> <mo>|</mo> <mo>|</mo> <msub> <mi>HF</mi> <mi>i</mi> </msub> <mo>|</mo> <mo>|</mo> </mrow> <mi>F</mi> </msub> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow></math>

Wherein phi denotes a codebook set, | - |_FRepresenting taking the Frobenius norm of the matrix. And if the judgment result shows that the F is the optimal precoding matrix, the serial number i of the optimal precoding matrix in the codebook is fed back to the sending end.

Disclosure of Invention

In the background section, the orthogonal space-time block coding in the above example is one of orthogonal space-time coding, and the orthogonal property of orthogonal space-time coding has the characteristic of not changing the channel distribution property. Meanwhile, the unitary matrix also has the characteristic of not changing the distribution characteristic of the channel. In fact, if it is desired to encode without changing the channel distribution characteristics, it is only necessary to perform encoding without changing the channel distribution characteristics once, and it is not necessary to perform such encoding twice or more. Therefore, if we use orthogonal space-time coding in MIMO-OFDM system, a non-unitary matrix can be used in precoding.

Meanwhile, in wireless transmission, it is always desirable to obtain better error rate performance under the same signal-to-noise ratio, that is, to obtain the signal-to-noise ratio gain as large as possible. The present invention provides a method, system and device for precoding with a non-unitary matrix in the foregoing system, so as to achieve better error rate performance without changing the channel distribution characteristics.

The specific implementation of the present invention provides a precoding method in a MIMO system, which uses orthogonal space-time coding, and uses more than two data streams, and includes:

selecting an optimal precoding vector from a beam forming codebook;

constructing a precoding matrix by adopting the optimal precoding vector;

and precoding by adopting the precoding matrix.

The invention also provides a MIMO system adopting limited feedback precoding, which comprises a transmitter and a receiver. The system adopts orthogonal space-time coding and adopts more than two data stream numbers; and,

the receiver includes:

the channel estimation unit is used for carrying out channel estimation and providing a channel estimation result to the judgment unit;

a codebook list storage unit for providing a precoding matrix or a precoding vector to the decision unit;

a decision unit, configured to select an optimal precoding vector from the beamforming codebook in the codebook list storage unit according to the channel estimation result provided by the channel estimation unit and a set decision criterion, and feed back information of the optimal precoding vector to the transmitter;

the transmitter includes:

a codebook list storage unit for providing a precoding matrix or a precoding vector to the precoding matrix construction unit;

a precoding matrix constructing unit, configured to select a corresponding precoding vector from a codebook list storage unit of the transmitter according to the optimal precoding vector information fed back by the receiver decision unit, and construct a precoding matrix;

and the precoding unit is used for precoding according to the precoding matrix constructed by the precoding matrix construction unit.

The present invention further provides a receiver used in a MIMO system, the receiver comprising:

the present invention further provides a transmitter for use in a MIMO system, wherein the transmitter comprises:

The invention provides a method, a system, a transmitter and a receiver for constructing a precoding matrix by using a beamforming codebook. The precoding matrix constructed by the beamforming codebook is a non-unitary matrix. Therefore, the method, the system, the transmitter and the receiver provided by the embodiments of the present invention can implement precoding by using a non-unitary matrix. After the method of the embodiment of the invention is used for precoding, the bit error rate performance better than that of a unitary matrix precoding scheme can be obtained, and the decoding complexity is lower through analysis.

Drawings

FIG. 1 is a diagram of a prior art limited feedback precoding MIMO-OFDM system;

FIG. 2 is a graph comparing the SNR and the BER for type I ideal feedback and type II ideal feedback in a low-speed moving environment with a maximum Doppler shift of 40;

fig. 3 is a graph comparing the snr and the ber obtained by simulating the (2, 1, 3) limited feedback provided by the embodiment of the present invention under the low-speed moving environment with the maximum doppler shift of 40 with the (2, 2, 3) limited feedback used in the prior art;

fig. 4 is a graph comparing the snr and the ber obtained by simulating the (2, 1, 6) limited feedback provided by the embodiment of the present invention under the low-speed moving environment with the maximum doppler shift of 40 with the (2, 2, 6) limited feedback used in the prior art;

fig. 5 is a graph comparing the relationship between the signal-to-noise ratio and the bit error rate obtained by simulating the (2, 1, 3) limited feedback provided by the embodiment of the present invention under the independent 12-path TU channel and the moving speed of 3km/h, respectively, with the (2, 2, 3) limited feedback condition adopted in the prior art;

fig. 6 is a graph comparing the relationship between the signal-to-noise ratio and the bit error rate obtained by simulating the (2, 1, 6) limited feedback provided by the embodiment of the present invention under the independent 12-path TU channel and the moving speed of 3km/h, respectively, with the (2, 2, 6) limited feedback condition adopted in the prior art;

fig. 7 is a schematic diagram of a MIMO system and apparatus using limited feedback precoding according to a third embodiment of the present invention.

Detailed Description

In order to make the technical solution of the present invention clearer, the following provides a specific embodiment of the present invention.

The first embodiment is as follows:

the first embodiment shows how to perform precoding by using a non-unitary matrix when orthogonal space-time coding is adopted in the MIMO-OFDM system. The method comprises the following specific steps:

after receiving the signal, the receiving end carries out channel estimation to obtain M_r×M_fThe channel matrix H. H may be obtained by any known channel estimation method, which is not described herein again; according to the number of transmitting antennas and the number of feedback bits, optimal judgment is carried out on a precoding matrix in a corresponding beam forming codebook set, an optimal transmitting vector v can be obtained, and the judgment is carried out according to the following formula:

<math><mrow> <mi>v</mi> <mo>=</mo> <munder> <mrow> <mi>arg</mi> <mi>max</mi> </mrow> <mrow> <msub> <mi>v</mi> <mi>i</mi> </msub> <mo>&Element;</mo> <mi>ζ</mi> </mrow> </munder> <msub> <mrow> <mo>|</mo> <mo>|</mo> <mi>H</mi> <msub> <mi>v</mi> <mi>i</mi> </msub> <mo>|</mo> <mo>|</mo> </mrow> <mn>2</mn> </msub> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>3</mn> <mo>)</mo> </mrow> </mrow></math>

wherein v is_iThe precoding vectors in the beamforming codebook, i.e. the codebook with the number of data streams equal to 1, are used. The beamforming codebook may be any codebook currently provided in the literature, and the present invention refers to the beamforming codebook in the draft ieee802.16e protocol.

After the optimal transmitting vector is obtained, the optimal precoding matrix can be constructed

F＝[v…v](4)

Equation (4) indicates that n optimal precoding vectors v are arranged in parallel to form an optimal precoding matrix F, and the value of n is the same as the number of data streams. And the transmitting end performs precoding by using the F.

The second embodiment is as follows:

the following takes Alamouti orthogonal space-time block coding received from closed-loop 2 transmit-receive 1 as an example to specifically describe the precoding method according to the present invention. For the purpose of comparing the performance of the embodiments of the present invention with the prior art in the following, it is assumed here that: the optimal precoding matrix generated by the prior art decision is F_IThe optimal precoding matrix generated by the method according to the embodiment of the invention is F_II。

In the MIMO-OFDM system adopting closed loop 2-to-1-to-receive Alamouti orthogonal space-time block coding, the number of transmitting antennas is 2, and because the optimal precoding matrix is constructed on the basis of the optimal precoding vector in the beamforming codebook in the present embodiment, when the feedback bit number is 3 bits, a vector is selected as the optimal precoding vector v in the (2, 1, 3) codebook set, and when the feedback bit number is 6 bits, a vector is selected as the optimal precoding vector v in the (2, 1, 6) codebook set. In the embodiment of the present invention, the decision criterion of v follows equation (3).

The codebooks are further described herein. When the number of feedback bits is 3 bits, this means that there are 8 different precoding vectors (or matrices) in the corresponding codebook. For example, there are 8 different precoding vectors in the (2, 1, 3) codebook. By analogy, there are 64 different precoding vectors in the (2, 1, 6) codebook, and v in equation (3)_iThe index i of (a) indicates the number of the vector in the codebook.

After the optimal transmitting vector v is generated by the judgment, the receiving end feeds back the judgment result, namely the serial number of the optimal transmitting vector v, to the transmitting end through a feedback channel.

The sending end receives the decision node fed back by the receiving endAfter the result, an optimal precoding matrix F is constructed according to the principle of the formula (4)_IIAnd precoding with the matrix.

The following describes the beneficial effects of the precoding method according to the embodiment of the present invention by taking the MIMO-OFDM system using closed-loop 2 transmit-receive Alamouti orthogonal space-time block coding as an example.

Because the theoretical performance analysis of the limited feedback is difficult, the lower limit of the error rate is given, namely the performance analysis under the ideal feedback. The precoding scheme in the IEEE802.16e protocol in the prior art is called as I-type closed-loop ideal feedback precoding, and the precoding matrix of the precoding scheme is F_IF is taken from (2, 2, 3) or (2, 2, 6) codebook according to different feedback bit numbers_I＝[v₁ v₂]，v₁、v₂All are 2 × 1 vectors, and are orthogonal to each other; the precoding scheme of the embodiment of the present invention is called II-type closed-loop ideal feedback precoding, and the precoding matrix is F_II，F_II＝[v v]V is taken from (2, 1, 3) or (2, 1, 6) codebook according to different feedback bit numbers, and is the optimal transmitting vector obtained through optimal judgment, which is also a 2 x 1 vector.

The 2-transmission 1-reception Alamouti orthogonal space-time block coding code word structure is

S = [\begin{matrix} s_{1} & {- s}_{2}^{*} \\ s_{2} & s_{1}^{*} \end{matrix}] - - - (5)

Wherein the first column vector is time t₁Signals transmitted from 2 transmitting antennas, the second column vector being time t₂Signals transmitted from 2 transmitting antennas, i.e.

{s_{t}}_{1} = {[\begin{matrix} s_{1} & s_{2} \end{matrix}]}^{T},

{s_{t}}_{2} = {[\begin{matrix} {- s}_{2}^{*} & s_{1}^{*} \end{matrix}]}^{T},

T denotes transposition. According to the Alamouti orthogonal space-time block coding hypothesis, t₁、t₂The same channel fading is experienced at the time, and the signal received by the receiving end can be represented as the signal in the case of the limited feedback precoding

{y_{t}}_{i} = \sqrt{\frac{1}{2}} {HFs}_{t}_{i} + {n_{t}}_{i}, i = 1,2 - - - (6)

Where H is a 1 × 2 actual channel matrix, H ═ H₁ h₂]，h₁、h₂Respectively representing the channel fading coefficients between the transmit antennas 1, 2 and the receive antennas,

representing gaussian white noise. In the embodiment of the present invention, it is assumed that the fading coefficients are independent and follow a complex gaussian distribution with a mean value of 0 and a variance of 1, that is, H is a rayleigh fading channel.

According to precoding and Alamouti orthogonal space-time block coding theory, equation (6) can be equivalent to the following form

Wherein,for 2 × 2 equivalent channel matrix H in equation (7)_effSingular Value Decomposition (SVD) is carried out to obtain H_eff＝U∑V^HWhere U is 1, V is 2 × 2 unitary matrix, and Σ is λ 0]λ is the equivalent channel matrix H_effAccording to the matrix singular value decomposition theory, there are

In the case of type I closed-loop ideal feedback precoding,F_I＝V＝[v₁ v₂]，HF_I＝[λ 0]the result after decoding is

{\hat{S}}_{I} = H_{eff}^{H} y

Wherein, (.)^HRepresents the transpose conjugate matrix of matrix solution, which is called as formula (8)

The first and second rows of the decoding branches, the signal of each branch is sent to a demodulator for demodulation after being decoded, and the error rate performance depends on the demodulation signal-to-noise ratio. According to equation (8), and assuming that the transmitted symbol power is normalized, i.e., ε_s1 and noise power 1, i.e.

It can be known that the demodulation signal-to-noise ratio of each branch after decoding is

In case of type II closed-loop ideal feedback precoding, F_II＝V＝[v v]，HF_II＝[λ λ]The result after decoding is

{\hat{S}}_{I} = H_{eff}^{H} y

After decoding, the signal-to-noise ratio of each branch is

It can be seen that the demodulation signal-to-noise ratio can be doubled by adopting the type II closed-loop ideal feedback precoding compared with the type I precoding, i.e. the system performance is improved by 3 dB. Because the traditional precoding method and the precoding method described in the specific embodiment of the present invention are actually the quantization of the type I and type II closed-loop ideal feedback precoding, if the quantization errors are the same, the difference between the two limited feedback precoding performances is also 3 dB. I.e. type II closed loop ideal feedback precoding has better error rate performance than type I.

Fig. 2, fig. 3 and fig. 4 show the bit error rate performance comparison between the method according to the embodiment of the present invention and the conventional precoding method under a low-speed mobile environment with a maximum doppler shift of 40, fig. 2 shows the performance comparison under an ideal feedback condition, fig. 3 shows the performance comparison between the scheme provided by the present invention and the prior art when 3 bits are fed back, and fig. 4 shows the performance comparison between the scheme provided by the present invention and the prior art when 6 bits are fed back. It can be seen that the method according to the embodiment of the present invention has a gain of about 3dB in comparison with the conventional precoding method when the signal-to-noise ratio is high in an independent single path rayleigh fading channel. In order to further verify the performance of the scheme of the invention under an independent multipath channel, fig. 5 and fig. 6 show the error rate performance comparison of the scheme of the invention and the conventional scheme when the moving speed is 3km/h under an independent 12-path TU channel, wherein the system carrier frequency is 3.5GHz, the bandwidth is 10MHz, and the number of points of fourier transform and cyclic prefix is 1024 and 128 respectively. Wherein, fig. 5 is a performance comparison between the scheme provided by the present invention and the prior art when 3 bits are fed back, and fig. 6 is a performance comparison between the scheme provided by the present invention and the prior art when 6 bits are fed back. As can be seen from fig. 5 and 6, the scheme of the present invention is still effective under independent multipath channels, and still can obtain about 3dB of gain compared with the conventional scheme under high snr.

Meanwhile, the improvement of the signal-to-noise ratio by the type-II closed-loop ideal feedback precoding is not at the cost of improving the total transmission power. According to the structure of Alamouti orthogonal space-time coding, t₁Total power of transmission at a time of

{| | \frac{1}{\sqrt{2}} {Fs}_{t_{1}} | |}_{2}^{2} = \frac{{| | {vs}_{1} + {vs}_{2} | |}_{2}^{2}}{2}

= \frac{{| | v | |}_{2}^{2} ({| s_{1} |}^{2} + {| s_{2} |}^{2})}{2} = 1

Wherein S is_tRepresents t₁Transmitted signal vector, t, of time Alamouti orthogonal space-time block coding₂The same theory can be used for the verification at all times. Therefore, the total transmission power is not increased by adopting the type II closed-loop ideal feedback precoding compared with the type I closed-loop ideal feedback precoding.

In addition, the precoding method of the embodiment of the invention can reduce the error rate of the system and the decoding complexity, which is caused by the same column vectors of the precoding matrix. Table 2 shows the comparison between the decoding complexity of the conventional precoding method and the precoding method according to the embodiment of the present invention when two data streams are received.

TABLE 2Aloumouti orthogonal STBC decoding complexity comparison

To implement the above method, the following provides a specific embodiment of a corresponding wireless communication system and apparatus.

The third embodiment of the present invention is described below with reference to fig. 7:

the third embodiment of the present invention provides a MIMO system with limited feedback precoding, which comprises a transmitter 710 and a receiver 720. The system employs orthogonal space-time coding and employs more than two data streams, and the receiver 720 includes:

a channel estimation unit 721 for performing channel estimation and providing the channel estimation result to the decision unit 723; besides, the channel estimation unit provides the channel estimation result to the decoder, but the role of the channel estimation unit in this respect is not directly related to the technical solution according to the present invention, and therefore should not be considered as a part of the technical solution described in this embodiment;

a codebook list storage unit 722 for providing the decision unit 723 with a precoding matrix or a precoding vector; in the embodiment of the present invention, the precoding vector may be selected from a beamforming codebook to construct a precoding matrix;

a decision unit 723, configured to select an optimal precoding vector from the beamforming codebook of the codebook list storage unit 722 according to the channel estimation result provided by the channel estimation unit 721 and a set decision criterion, and feed back information of the optimal precoding vector to the transmitter 710; the decision criterion for selecting the optimal precoding vector may follow equation (3).

Generally, different precoding vectors can be represented by different values, and the feedback only needs to feed back the value corresponding to the selected precoding vector, rather than feeding back the precoding vector itself to the transmitter. Of course, the information of the precoding vector described in the present embodiment is not limited to the above-mentioned corresponding numerical value, and may be fed back as long as the selected precoding vector can be correctly specified.

The transmitter 710 includes:

a codebook list storage unit 711 for providing the precoding matrix or the precoding vector to the precoding matrix construction unit 712;

a precoding matrix constructing unit 712, configured to select a corresponding precoding vector from the codebook list storage unit 711 according to the optimal precoding vector information fed back by the determining unit 723 of the receiver 720, and construct a precoding matrix; the construction of the precoding matrix from the precoding vector follows the principle of equation (4).

A precoding unit 713, configured to perform precoding according to the precoding matrix constructed by the precoding matrix constructing unit 712.

The above embodiments also provide a transmitter and a receiver applied to the method of the present invention.

Any modification, equivalent replacement, improvement, etc. made to the method, system and apparatus described in the embodiments of the present invention within the spirit and principle of the embodiments of the present invention should be included in the protection scope of the present invention.

Claims

1. A precoding method in a MIMO system is characterized by adopting orthogonal space-time coding and more than two data streams, and comprises the following steps:

selecting an optimal precoding vector from a beam forming codebook;

constructing a precoding matrix by adopting the optimal precoding vector;

and precoding by adopting the precoding matrix.

2. The method of precoding in a MIMO system of claim 1, wherein the optimal precoding vector is selected from the beamforming codebook according to the following principle,

<math><mrow> <mi>v</mi> <mo>=</mo> <munder> <mrow> <mi>arg</mi> <mi>max</mi> </mrow> <mrow> <msub> <mi>v</mi> <mi>i</mi> </msub> <mo>&Element;</mo> <mi>ζ</mi> </mrow> </munder> <msub> <mrow> <mo>|</mo> <mo>|</mo> <mi>H</mi> <msub> <mi>v</mi> <mi>i</mi> </msub> <mo>|</mo> <mo>|</mo> </mrow> <mtext>2</mtext> </msub> </mrow></math>

wherein v is an optimal precoding vector; v. of_iA precoding vector in a beam forming codebook, namely a codebook with the data stream number equal to 1; h is a channel matrix; i | · | purple wind₂The expression takes the vector 2 norm.

3. The method of precoding in a MIMO system of claim 2, wherein the beamforming codebook is a beamforming codebook in an ieee802.16e protocol.

4. The precoding method in the MIMO system of claim 1, wherein the constructing the precoding matrix using the optimal precoding vector is performed by arranging n optimal precoding vectors in parallel to form a precoding matrix, and a value of n is the same as a number of data streams.

5. A MIMO system adopting limited feedback precoding comprises a transmitter and a receiver, and is characterized in that the system adopts orthogonal space-time coding and adopts more than two data stream numbers; and,

the receiver includes:

the transmitter includes:

6. The MIMO system with limited feedback precoding of claim 5, wherein the information of the optimal precoding vector fed back by the feedback unit is a value corresponding to each precoding vector.

7. A receiver for use in a MIMO system, the receiver comprising:

8. the receiver of claim 7, wherein the decision unit selects the optimal precoding vector in the beamforming codebook according to the following principle:

9. A transmitter for use in a MIMO system, the transmitter comprising:

10. The transmitter of claim 9, wherein the precoding matrix construction unit constructs a precoding matrix using the optimal precoding vector information, and comprises:

determining an optimal precoding vector according to the optimal precoding vector information;

and paralleling n optimal precoding vectors to form a precoding matrix, wherein the value of n is the same as the number of data streams.