KR101016068B1 - Apparatus and method for Channel Estimation in Multi Input Multi Out system - Google Patents

Abstract

The present invention relates to an apparatus and method for estimating a channel in a multiplex transmission system. The present invention relates to a pilot around a subcarrier to estimate channel information in a multiplex transmission system. An apparatus and method for estimating a channel in a multiplex transmission system for reducing bit error probability by estimating channel information of a subcarrier using a vector after being expressed as a vector are provided.

To this end, the present invention provides a channel estimation method, comprising: selecting a pilot adjacent to a subcarrier and generating a vector; Calculating a first connection vector connecting the pilot closest to the subcarrier (hereinafter, the nearest pilot) and the first pilot among the selected pilots, and a second connection vector connecting the nearest pilot and the second pilot; Calculating a third connection vector between the nearest pilot and the subcarrier using the calculated first and second connection vectors; Calculating a first cross product between the first connection vector and the second connection vector; Calculating a second cross product between the first connection vector and the third connection vector; And estimating channel information of the subcarrier using the calculated first and second cross products.

Multiple Transmission System, Channel Estimation, Connection Vector, Pilot, Cross Product

Description

Apparatus and method for Channel Estimation in Multi Input Multi Out system

The present invention relates to an apparatus and method for estimating a channel in a multiplex transmission system. More particularly, the present invention relates to a pilot sequence around a subcarrier to estimate channel information in a multiplex transmission system. The present invention relates to a channel estimating apparatus and method in a multiplex transmission system for reducing bit error probability by expressing a channel information of a subcarrier using a vector including information.

Interpolation to be used in the present invention means estimating values at various time positions between the predetermined time intervals using a plurality of values obtained with a predetermined time interval.

Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard based mobile communication system, for example, WiBro (Wireless Broadband) provides a high-speed Internet service (Portable Internet) during the move.

In particular, the IEEE 802.16 standard proposes a MIMO (Multi-Input Multi-Output) transmission scheme for increasing data throughput. In the MIMO transmission method, the base station transmits different information through two different antennas, and the terminal receives the information through one or two antennas and then detects the information through a MIMO decoding process.

The IEEE 802.16 standard is a mobile communication standard based on an orthogonal frequency division multiple access (OFDMA) scheme. On the transmitting side, a user's data to be transmitted is transmitted by subcarriers according to frequency and by orthogonal frequency division multiplex (OFDM) symbols according to time. Send separately.

Then, the receiving side estimates channel size information (value) and phase information (value) required for data demodulation using a pilot signal received through a specific subcarrier of a specific symbol determined by the standard. This process is called channel estimation.

The MIMO transmission method has a smaller number of pilot signals than the conventional single input single output (SISO) transmission method. This is because pilot signals must be received from different transmit antennas, respectively. Channel estimation using such a small number of pilot signals is very poor in performance.

In the conventional MIMO transmission method, a channel estimation method estimates a channel using interpolation. Of course, there are various channel estimation methods in addition to the interpolation method, but in general, the interpolation method which is very small and has excellent performance is mainly used.

1 is a diagram illustrating an embodiment of a channel estimation method using a conventional interpolation method.

First, suppose that a frequency period k to k + 13 and a time period n to n + 11 are allocated for a specific user. At this time, a pilot signal for each transmit antenna determined by the standard is defined within the allocated section.

In addition, the position of the filled circle 101 is the position of the pilot signal transmitted through a specific antenna, it is represented in the form of a pattern. The location of the unfilled circle 102 represents the location of the data to be sent to the user.

As shown in FIG. 1, first interpolation using a pilot signal is performed based on a location of a specific subcarrier, for example, k, k + 4, k + 8, and k + 12 axes. Through this, the channel at all OFDM symbol positions corresponding to the specific subcarrier position is estimated. That is, channel information of subcarriers located on four horizontal lines in the corresponding section is estimated.

Subsequently, the information on the channel corresponding to the k + 1, k + 2, and k + 3th subcarriers is estimated using the estimated channel information corresponding to the k, k + 4th subcarriers for each OFDM symbol (secondary interpolation). ). That is, the channel information of the subcarrier located on the straight line in the vertical direction is estimated in the corresponding section.

In this way, the channels corresponding to all subcarriers are estimated in the frequency section and the time section assigned to the user.

Hereinafter, a channel estimation method using a conventional interpolation method will be described in more detail.

As an example, the channel information of the subcarriers on the k th axis of the frequency section and the n + 7 th axis from the n th axis of the time section is obtained.

First, the difference between the channel information of the subcarrier (pilot signal) on the kth axis of the frequency section and the n + 3 axis of the time section and the channel information of the subcarrier (pilot signal) on the n + 7th axis is obtained. Divide by the difference. This may be expressed as in Equation 1 below.

Channel information (values) at all OFDM symbol positions are obtained by using a difference of channel information (values) between subcarriers obtained in Equation 1 above. This may be expressed as in Equation 2 below.

In this way, channel information at the positions of the remaining OFDM symbols on the k, k + 4, k + 8 and k + 12th axes can be obtained.

Subsequently, channel information of subcarriers in k, k + 4, k + 8, and k + 12th axes of the nth axis is estimated by applying the same method (first order interpolation).

In the conventional channel estimation method using the interpolation method, a deviation occurs in the accuracy of channel estimation for each subcarrier corresponding to a frequency section and a time section. That is, as shown in (a) of FIG. 3, it can be seen that the degree of bit error probability is particularly high at the boundary (dotted line) of the allocation section.

As a result, the conventional channel estimation method using interpolation has a problem that the bit error probability is increased at the boundary of the allocation interval, thereby reducing the reception performance.

It is an object of the present invention to solve this problem.

Accordingly, the present invention represents a pilot around a subcarrier to estimate channel information in a multiplex transmission system as a vector including a sequence on a time axis, a sequence on a frequency axis, and channel information of the pilot, and then estimates channel information of the subcarrier using the vector. Accordingly, an object of the present invention is to provide an apparatus and method for estimating a channel in a multiplex transmission system for reducing a bit error probability.

The objects of the present invention are not limited to the above-mentioned objects, and other objects and advantages of the present invention which are not mentioned can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

According to an aspect of the present invention, there is provided an apparatus for estimating a channel in a multiplex transmission system, the apparatus comprising: vector generating means for selecting a pilot adjacent to a subcarrier and generating a vector; The first connection vector and the second connection vector for connecting the pilot (closest pilot) closest to the subcarrier and the first and second pilots, respectively, are calculated using the vector generated by the vector generating means. Connection vector calculating means for calculating a third connection vector between the adjacent pilot and the subcarrier; Cross product calculating means for calculating a first cross product between the first connection vector and the second connection vector and the second cross product between the first connection vector and the third connection vector calculated by the connection vector calculating means; And channel information estimating means for estimating channel information of the subcarrier using the first and second cross products calculated by the cross product calculating means.

In addition, the method of the present invention for achieving the above object, the channel estimation method, comprising the steps of: generating a vector by selecting a pilot close to the subcarrier; Calculating a first connection vector connecting the pilot closest to the subcarrier (hereinafter, the nearest pilot) and the first pilot among the selected pilots, and a second connection vector connecting the closest pilot and the second pilot; Calculating a third connection vector between the nearest pilot and the subcarrier using the calculated first and second connection vectors; Calculating a first cross product between the first connection vector and the second connection vector; Calculating a second cross product between the first connection vector and the third connection vector; And estimating channel information of the subcarrier using the calculated first and second cross products.

In addition, since the estimation error increases when estimating a channel using only a pilot signal of a specific frequency axis at an interface of an allocation interval, the channel is estimated by using a pilot signal existing in a subcarrier neighbor.

In addition, the present invention is applied to a receiver of a terminal that supports a multi-input multi-output (MIMO) transmission method of a mobile communication system based on the IEEE 802.16 standard, by optimally utilizing a pilot signal for the MIMO transmission method In addition, the present invention provides an improved channel estimation scheme and thus an improved MIMO reception performance.

At this time, the receiver separates the received signals into pilot symbols and data symbols through a matched filter, estimates a channel using the pilot symbols, and uses the estimated result to estimate the channel of the data symbols. To enable channel estimation for data symbols, interpolation is used and the data is recovered using the results.

In the present invention as described above, a pilot around a subcarrier to estimate channel information in a multiplex transmission system is expressed as a vector including the order on the time axis, the order on the frequency axis, and the channel information of the pilot, and then using the channel information of the subcarrier. By estimating, there is an effect that the bit error probability can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings, It can be easily carried out. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is an exemplary explanatory diagram of a channel estimation method in a multi-transmission system according to the present invention, and uses plane equations for channel estimation.

For example, consider a case of obtaining channel information of a subcarrier in a k-th axis of a frequency section and an n-th axis of a time section.

First, the channel information of the pilot on the k-th axis of the frequency section and the n + 3-th axis of the time section is p ₁ [x ₁ y ₁ z ₁ ], and on the k + 4th axis and the n + 1th axis of the frequency section. The channel information of the pilot in p ₂ [x ₂ y ₂ z ₂ ], and the channel information of the pilot in frequency interval k + 4th axis and time interval n + 5th axis p ₃ [x ₃ y ₃ z ₃ ] It is expressed in vector form as

Here, the first term of the vector indicates the order on the time axis, the second term indicates the order on the frequency axis, and the last term indicates channel information of each pilot.

Subsequently, when a vector connecting the pilot p ₁ and the pilot p ₂ is a and a vector connecting the pilot p ₁ and the pilot p ₃ is b, the vector c connecting the subcarrier and the pilot p ₁ to be obtained is as follows. Equation 3] is represented.

Then, the cross product of the vectors a and b is obtained through Equation 4.

In addition, the cross product of the vectors a and c is obtained through Equation 5.

Subsequently, the channel information of the subcarrier to be obtained using the d vector obtained in Equation 4 and the cross product obtained in Equation 5 is expressed as Equation 6 below.

Here, z is obtained as shown in Equation 7 below.

As shown in (b) of FIG. 3, the channel information estimated through this process has less variation in the boundary of the allocation interval, thereby reducing the bit error probability, thereby improving reception performance.

That is, the reception performance (bit error probability) when demodulating data using the mean square error of the channel estimation error and the estimated channel information is improved.

4 is a flowchart illustrating a channel estimation method in a multiplex transmission system according to the present invention.

First, three pilots adjacent to a subcarrier for which channel information is to be estimated are selected and expressed as a vector (401). In this case, the first term of each vector represents the order on the time axis, the second term represents the order on the frequency axis, and the last term represents channel information of each pilot.

Thereafter, a first connection vector connecting the pilot closest to the subcarrier (hereinafter, the nearest pilot) and the first pilot among the selected pilots and a second connection vector connecting the closest pilot and the second pilot are calculated ( 402).

Thereafter, a third connection vector between the nearest pilot and the subcarrier is calculated using the calculated first and second connection vectors (403).

Thereafter, a first cross product between the calculated first connection vector and the second connection vector is calculated (404).

Thereafter, a second cross product between the calculated first connection vector and the third connection vector is calculated (405).

Thereafter, the channel information of the subcarrier is estimated using the calculated first and second cross products (406).

5 is a diagram illustrating an embodiment of a channel estimating apparatus in a multiplex transmission system according to the present invention.

As shown in FIG. 5, the apparatus for estimating a channel in a multiplex transmission system according to the present invention includes a vector generator 51 for selecting and expressing three pilots close to a subcarrier to estimate channel information as a vector. A first connection vector connecting a pilot (hereinafter, nearest nearest pilot) and a first pilot closest to the subcarrier using a vector generated by the vector generator 51, and a first connection vector connecting the closest pilot and the second pilot; After the second connection vector is calculated, a connection vector calculator 52 for calculating a third connection vector between the nearest pilot and the subcarrier and the first connection vector and the second calculated by the connection vector calculator 52 A cross product calculating unit 53 for calculating a first cross product between the connection vectors and a second cross product between the first connection vector and the third connection vector, and the first and second non products calculated by the cross product calculating unit 53. And a channel information estimating unit 54 for estimating channel information of the subcarrier using an enemy.

6 is a diagram illustrating an exemplary performance analysis of a channel estimation method in a multiplex transmission system according to the present invention.

Here, 'LI-60-6p' represents a channel estimation error according to the conventional method, and 'Pr- 60-6p' represents a channel estimation error according to the present invention.

FIG. 7 is a performance analysis diagram of another embodiment of a channel estimation method in a multiplex transmission system according to the present invention, and illustrates a bit error probability according to a signal-to-noise ratio at a terminal movement speed of 120 km / h.

Here, 'LI, 120' represents a bit error probability according to the conventional method, and 'Proposed, 120' represents a bit error probability according to the present invention.

On the other hand, the method of the present invention as described above can be written in a computer program. And the code and code segments constituting the program can be easily inferred by a computer programmer in the art. In addition, the written program is stored in a computer-readable recording medium (information storage medium), and read and executed by a computer to implement the method of the present invention. The recording medium may include any type of computer readable recording medium.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

1 is a diagram illustrating an embodiment of a channel estimation method using a conventional interpolation method.

2 is a diagram illustrating an embodiment of a channel estimation method in a multiplex transmission system according to the present invention;

Figure 3 is an exemplary view showing the degree of improvement in reception performance according to the present invention in comparison with the conventional method,

4 is a flowchart illustrating a channel estimation method in a multiplex transmission system according to the present invention.

5 is a diagram illustrating an embodiment of a channel estimating apparatus in a multiplex transmission system according to the present invention;

6 is a diagram illustrating a performance analysis of a channel estimation method in a multiplex transmission system according to the present invention;

7 is a diagram illustrating another embodiment of a channel estimation method in a multiplex transmission system according to the present invention.

* Explanation of symbols for the main parts of the drawings

51: vector generator 52: connection vector calculator

53: external product calculation unit 54: channel information estimation unit

Claims (12)

In the channel estimation method, Selecting a pilot proximate to a subcarrier and generating a vector including an order on a time axis, an order on a frequency axis, and channel information of the pilot; Calculating a first connection vector connecting the pilot closest to the subcarrier (hereinafter, the nearest pilot) and the first pilot among the selected pilots, and a second connection vector connecting the nearest pilot and the second pilot; Calculating a third connection vector between the nearest pilot and the subcarrier; Calculating a first cross product between the first connection vector and the second connection vector; Calculating a second cross product between the first connection vector and the third connection vector; And Estimating channel information of the subcarrier using the calculated first and second cross products. Channel estimation method in a multiple transmission system comprising a. delete The method of claim 1, The connection vector calculating step, A channel estimation method in a multiplex transmission system, wherein the first connection vector (a), the second connection vector (b), and the third connection vector (c) are calculated using Equation A below. Equation A

Here, (x ₁ , y ₁ , z ₁ ) means a vector of the nearest pilot, (x ₂ , y ₂ , z ₂ ) means a vector of the first pilot, and (x ₃ , y ₃ , z ₃ ) means a vector of a second pilot, and (x, y, z) means a vector of the subcarrier. Also, the first term in () indicates the order on the time axis, the second term in () indicates the order on the frequency axis, and the third term in () indicates the channel information. The method of claim 3, wherein The first cross product calculating step, A channel estimation method in a multiplex transmission system, characterized in that it is calculated by the following Equation B. Equation B

here,

Represents the cross-product operation of the vector. The method of claim 4, wherein The second cross product calculating step, A channel estimation method in a multiple transmission system, characterized in that it is calculated by the following Equation C. Equation C

The method of claim 5, Channel information estimation step of the subcarrier, A channel estimation method in a multiplex transmission system, characterized by estimating channel information (z) through a plane equation and [Equation D] below. [Equation D]

In the channel estimation apparatus in a multiplex transmission system, Vector generating means for selecting a pilot proximate to a subcarrier and generating a vector including an order on a time axis, an order on a frequency axis, and channel information of the pilot; Using the vector generated by the vector generating means, a first connection vector and a second connection vector for connecting the pilot closest to the subcarrier (hereinafter, the nearest pilot) and the first and second pilots, respectively, are calculated, and the nearest Connection vector calculating means for calculating a third connection vector between a pilot and the subcarrier; Cross product calculating means for calculating a first cross product between the first connection vector and the second connection vector and the second cross product between the first connection vector and the third connection vector calculated by the connection vector calculating means; And Channel information estimating means for estimating channel information of the subcarrier using the first and second cross products calculated by the cross product calculating means Channel estimation apparatus in a multiple transmission system comprising a. delete The method of claim 7, wherein The connection vector calculation means, And a first connection vector (a), a second connection vector (b), and a third connection vector (c) are calculated using Equation A below. Equation A

Here, (x ₁ , y ₁ , z ₁ ) means a vector of the nearest pilot, (x ₂ , y ₂ , z ₂ ) means a vector of the first pilot, and (x ₃ , y ₃ , z ₃ ) means a vector of the second pilot, and (x, y, z) means a vector of the subcarrier. Also, the first term in () indicates the order on the time axis, the second term in () indicates the order on the frequency axis, and the third term in () indicates the channel information. The method of claim 9, The external product calculating means, An apparatus for estimating a channel in a multiplex transmission system, wherein the first cross product is calculated through Equation B below. Equation B

here,

Represents the cross-product operation of the vector. The method of claim 10, The external product calculating means, A channel estimation apparatus in a multiplex transmission system, wherein the second cross product is calculated through Equation C below. Equation C

The method of claim 11, The channel information estimating means, A channel estimating apparatus in a multiplex transmission system, characterized by estimating channel information z through a plane equation and Equation D below. [Equation D]

Images