KR20160100806A - Channel Estimation Method in Wireless Communication System using Beamforming Scheme - Google Patents

Abstract

In order to reduce overhead and improve SNR performance in a beamforming system such as multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) systems, To a channel estimation method in a wireless communication system in which only a valid channel is estimated at a receiving end so as to enable decoding using an effective channel.

Description

[0001] The present invention relates to a channel estimation method in a wireless communication system using a beamforming technique,

The present invention relates to a channel estimation technique in a wireless communication system, and more particularly, to a pilot transmission and channel estimation technique in a wireless communication system such as a multiple input single output system using a beamforming technique.

A channel estimation technique using a training sequence such as a pilot signal is widely used in a wireless communication system such as an LTE (Long Term Evolution) system. When estimating a channel using a training sequence in a multiple-input single-output (MISO) system or a multiple-input multiple-output (MIMO) system, the conventional technique is such that each transmitting antenna transmits orthogonal training sequences To estimate the channel of each transmission / reception path. However, because of this, the conventional technique has a disadvantage in that it has a high overhead since it transmits a training sequence a number of times proportional to the number of transmission antennas.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to reduce overhead in a beamforming system such as multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) In a wireless communication system in which a transmitting end simultaneously transmits a training sequence using a beamformed training sequence and a receiving end estimates only an effective channel and enables decoding using an effective channel for pilot transmission and channel estimation capable of improving SNR performance, Channel estimation method.

The technical problems of the present invention are not limited to the above-mentioned technical problems, and other technical problems which are not mentioned can be understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided a channel estimation method in a wireless communication system, the method comprising: generating a beamformed single training sequence by performing beamforming in a transmitter; ; And concurrently transmitting the beamformed single training sequence at the transmitter via a plurality of transmit antennas, the generating comprising deriving a transmit beamforming coefficient for each channel for the plurality of transmit antennas ; And generating, for each channel, the transmission beamforming coefficients multiplied by a training sequence of each channel as the beamformed single training sequence.

The wireless communication system may include multiple-input single-output (MISO) or multiple-input multiple-output (MIMO).

The wireless communication system may include a time division duplexing (TDD) system.

In this case, based on the training sequence of each channel received from the receiver, the transmitter estimates a channel parameter of each channel to derive a transmission beamforming coefficient of each channel.

The wireless communication system may include a Frequency Division Duplexing (FDD) system.

In this case, if the receiver estimates and feeds back the channel parameters of the respective channels based on the training sequence of the channels transmitted by the transmitter, based on the channel parameters of the channels received from the receiver, And derives a transmission beamforming coefficient of each channel.

The channel estimation method in the wireless communication system is characterized in that the receiver estimates the effective channel vector reflecting the channel parameter of each channel and the transmission beamforming coefficient of each channel and decodes the received data using the effective channel vector have.

According to the channel estimation technique in the wireless communication system according to the present invention, in a beamforming system such as multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) By using a sequence to transmit at the same time, overhead for channel re-estimation can be greatly reduced.

The performance of the wireless communication system such as the SNR performance in the delayed channel environment is greatly improved through decoding using the effective channel by estimating only the effective channel according to the channel re-estimation at the receiving end.

1 is a view for explaining beamforming in a general wireless communication system.
FIGS. 2A and 2B are diagrams for explaining a channel estimation process in a conventional TDD (Radio Frequency Division Multiple Access) wireless communication system.
FIGs. 3A and 3B are diagrams for explaining a channel estimation process at a transmitting / receiving end of a wireless communication system according to an embodiment of the present invention.
FIG. 4 illustrates system performance in a delay channel when a channel estimation scheme of a wireless communication system according to an embodiment of the present invention is applied to transmission beamforming and decoding.
FIG. 5 illustrates system performance in a delay channel when a channel estimation scheme of a wireless communication system according to an embodiment of the present invention is applied to transmission beamforming and decoding is performed using a re-estimated channel.

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference numerals whenever possible, even if they are shown in different drawings. In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the difference that the embodiments of the present invention are not conclusive.

In describing the components of the embodiment of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. Also, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art and are to be interpreted in an ideal or overly formal sense unless explicitly defined in the present application Do not.

1 is a view for explaining beamforming in a general wireless communication system.

1, a transmitter (Tx) of a general radio communication system transmits a training sequence orthogonal to each other through L transmission antennas (Tx1, Tx2, ..., TxL) ) Received these signals using one antenna and estimated the respective channel parameters h ₁ , .., h _L. However, such a conventional technique results in a high overhead since the training sequence is transmitted a number of times proportional to the number of transmission antennas.

FIGS. 2A and 2B are diagrams for explaining a channel estimation process in a conventional TDD (Radio Frequency Division Multiple Access) wireless communication system.

As shown in FIG. 2A, the receiver Rx sends the training sequence s _t = {s _{t , 1} , ..., s _{t , M} } to the transmitter _{T x} . Where M represents the length of the transmitter (Tx) training sequence.

As shown in FIG. 2B, the transmitter Tx uses channel reciprocity characteristics from the training sequence s _t = {s _{t, 1} , .., s _{t , M} } received from the receiver R x to calculate channel parameters h ₁ , .., h _L , and derives the transmission beamforming coefficients w ₁ ^* , .. w _L ^* of each channel (* is a complex conjugate). The transmitter (Tx) sends the beamforming coefficients w ₁ ^*, .. w _L ^* beamforming a signal h _l w _l ^* x x a transmission target data signal of each channel by using a channel of each derived.

At this time, the receiver Rx receives a signal y transmitted from the L transmission antennas Tx1, Tx2, ..., TxL using one antenna as shown in Equation (1) ). The receiver Rx obtains the channel parameters h ₁ , .., h _L through channel estimation in order to extract and decode the data signal x from the received signal y.

 [Equation 1]

However, in the conventional channel estimation technique, in order to estimate the channel parameters h ₁ , .., h _L in Equation (1), each transmission antenna (Tx1, Tx2, ..., TxL) To transmit the training sequence s _{t , l} of each channel orthogonally to each other.

If the transmitter (Tx) transmits s _{t , l} to the l th transmit antenna, the receiver (Rx) estimates h _l from the received signal vector y _l = h _l s _{t , l} + n _l . The transmitter Tx performs this process for each of the transmit antennas and then the receiver Rx estimates the transmit and receive period channel parameter vector h as shown in Equation 2 to obtain the received signal y from Equation 1 as x And decodes it.

&Quot; (2) "

In the present invention, in a wireless communication system using beamforming such as multiple-input single-output (MISO) and multiple-input multiple-output (MIMO), the overhead in the conventional art is reduced and a signal- For the pilot transmission and channel estimation, which can improve performance, the transmitter transmits simultaneously using a beamformed single training sequence, and only the effective channel is estimated in the receiver so that decoding using the effective channel is enabled.

FIGs. 3A and 3B are diagrams for explaining a channel estimation process at a transmitting / receiving end of a wireless communication system according to an embodiment of the present invention.

As shown in FIG. 3A, a receiver Rx of a wireless communication system according to an embodiment of the present invention transmits a training sequence s _t = {s _{t , 1} , .. s _{t , M} } to a transmitter Tx. Where M (positive integer) indicates the length of the transmitter (Tx) training sequence.

As shown in FIG. 3B, the transmitter Tx uses the channel reciprocity characteristic from the training sequence s _t = {s _{t, 1} , .., s _{t , M} } received from the receiver _{R x ,} h ₁ , .., h _L , and then derives the transmission beamforming coefficients w ₁ ^* , .. w _L ^* of each channel (* is a complex conjugate) using the estimated channel parameters. The transmitter (Tx) is the transmit antennas in the beamforming coefficients for each channel derived ^{_{w 1 *, .. w L *}} L pieces (L is a positive integer) by using the (Tx1, Tx2, ..., TxL ) the (Set) vector s _t = {s _{t , 1} , .. s _{t , M} } to each channel.

That is, in order to estimate the channel in the receiver Rx, the transmitter of the present invention uses a beamforming technique to generate a single training sequence vector s _t = {s _{t , 1 ,.} . s _{t , M} } at the same time. In this case, a single training sequence beamformed is transmitted in each of the transmit antennas (Tx1, Tx2, ..., TxL) is the value obtained by multiplying a training sequence of transmission beamforming coefficient and each channel on the channel L (w _l ^* s _t ).

Accordingly, the signal y received by the receiver Rx is expressed by Equation (3).

&Quot; (3) "

The receiver Rx can estimate the effective channel vector beta, not the channel vector h, from the received signal y as in Equation (3) as in Equation (4).

&Quot; (4) "

로부터 x를 추출해 디코딩한다. Thereafter, the transmitter (Tx) that transmits the signal h _l w _l ^* x beamforming a transmission subject data signal x. At this time, the receiver Rx receives a signal y transmitted from the L transmission antennas Tx1, Tx2, ..., TxL using one antenna, as shown in Equation (1) n). The receiver Rx removes the noise vector n and uses the estimated effective channel vector?

And decodes x.

Meanwhile, beam forming training sequence according to the present invention is an effective channel estimation techniques, and can be applied to a TDD (Time Division Duplexing) system as described above, in addition to (Frequency Division Duplexing) FDD system using a w _l ^* s _t Can also be used for channel re-estimation for decoding of received data.

을 피드백한다.That is, in Figure 3a, if the Figure 3b operating in FDD system, the transmitter (Tx) is the transmission antennas (Tx1, Tx2, ..., TxL) orthogonal to the training sequence with _{s t = {s t, 1} , s _{t .., M}} When the transmission, the receiver (Rx) is a channel parameter estimation vector to the transmitter (Tx) and then estimating the respective transmit-receive antenna channel parameters h _1, h .. _L between

Lt; / RTI >

을 이용하여 데이터 전송을 위해 빔포밍을 수행하여 빔포밍 계수 벡터 w^H를 구하고 빔포밍된 훈련 시퀀스는 w_l ^*s_t를 전송한다. 수신기(Rx)는 추정한 유효 채널 벡터 β 기반의 유효 채널을 이용하여 수신 데이터 신호

로부터 x를 디코딩할 수 있다. The transmitter Tx outputs a feedback estimated channel value, i.e., a channel parameter vector

The beamforming coefficient vector w ^H is obtained by performing beamforming for data transmission, and the beamformed training sequence transmits w _l ^* s _t . The receiver Rx uses the estimated effective channel vector < RTI ID = 0.0 >

≪ / RTI >

FIG. 4 illustrates system performance in a delay channel when a channel estimation scheme of a wireless communication system according to an embodiment of the present invention is applied to transmission beamforming and decoding.

If the channel is changed between the time when the channel is estimated and the time when the actual data is transmitted and received, that is, when the delayed channel information is used for beamforming and decoding, the performance of the system may be significantly degraded. 4 shows an example between SNR and transmitter power (Pout) when a delayed channel is used for transmit beamforming and decoding. In the example of FIG. 4, when the correlation coefficient between the delay channel and the channel to which the actual data is transmitted is 0.9, the system performance is not improved even when the transmission power is increased in the high signal-to-noise ratio (SNR) Can be seen.

However, if the orthogonal training sequence is used for channel re-estimation as in the conventional technique, much overhead can be generated. In order to solve this problem, the present invention proposes a technique of reordering a channel to be used for data decoding of a receiving end using the beamformed training sequence technique.

FIG. 5 illustrates system performance in a delay channel when a channel estimation scheme of a wireless communication system according to an embodiment of the present invention is applied to transmission beamforming and decoding is performed using a re-estimated channel.

In the example of FIG. 5, the system performance is remarkably improved when a channel re-estimated based on the effective channel vector? Is used for decoding according to the present invention, as compared with FIG. The example of FIG. 5 assumes a correlation coefficient of 0.9 between the delay channel and the channel to which the actual data is transmitted, as shown in FIG.

As described above, in a wireless communication system according to an embodiment of the present invention, in a beamforming system such as multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) The receiver Rx estimates only the effective channel according to the channel re-estimation, and then decodes it using the effective channel. The performance of the wireless communication system such as the SNR performance in the delayed channel environment is greatly improved.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention.

Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Transmitter (Tx)
Transmit antennas Tx1, Tx2, ..., TxL,
Receiver (Rx)
The channel parameters (h ₁ , .. h _L )
The training sequence s _t = {s _{t , 1} , .. s _{t , M} }
The beamformed training sequence is w _l ^* s _t

Claims (1)

A channel estimation method in a wireless communication system,
Performing beamforming at a transmitter to generate a beamformed single training sequence; And
Concurrently transmitting the beamformed single training sequence at the transmitter via a plurality of transmit antennas,
Wherein the generating comprises:
Deriving a transmit beamforming coefficient of each channel for the plurality of transmit antennas; And
Generating a beamformed training sequence for each channel by multiplying the transmission beamforming coefficient by a training sequence of each channel;
Wherein the channel estimating method comprises:

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